Background: The treatment of serious drug or chemical poisoning relies mostly on the use of standard intensive care measures. Whereas mortality from poisoning is generally low, exposure to drugs and chemicals is common, and the toxicologist is often faced with management decisions regarding extracorporeal removal of drugs and toxins. Although very few poisonings require, or are effectively treated by extracorporeal elimination procedures, these procedures may be lifesaving in selected poisoning. This paper will discuss the role of dialysis and its newer modalities (high-efficiency and high-flux dialysis) in the management of poisoning together with other techniques used in treating poisoned patients, such as hemofiltration—continuous arteriovenous hemofiltration (CAVH), continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodiafiltration (CVVHD). Hemodialysis: The use of hemodialysis in the treatment of poisoning dates back to the middle of the twenty century. Hemodialysis was first used in 1950 by Doolan in patient poisoned with salicylates. This was followed by extensive use of hemodialysis in the treatment of barbiturate overdose, the major cause of intoxication of that decade (1). Numerous reports appeared in the literature at the 1950s, 1960s and 1970s of the efficacy of hemodialysis for the treatment of poisoning, but it was found that the limitations of hemodialysis in the removal of endogenous toxins also applied to its use in poisoning with exogenous substances. Hemodialysis is the process in which the blood is circulated through a system in which a semi-permeable membrane separates the components of the blood from the constituents of the dialysis fluid. The diffusion of dialyzable substances across the membrane, from an area of high concentration to an area of low concentration, allows their removal. Chemical and drug removal by dialysis is determined by dialyzer conditions (blood flow rate, dialysate flow rate, dialyzer surface area, and pore structure of the chosen membrane) and by toxicokinetic factors of the toxic substances. Toxicodynamic factors may also be important if cardiovascular function is impaired. The characteristics that predict the successful removal of a toxic agent by dialysis include low volume of distribution ( < 1 L/kg), the presence of the toxin in the central compartment, low endogenous clearance, a low molecular weight ( < 500 daltons), low protein binding and high water solubility. To be clinically effective dialysis should improve the removal of a toxin by at least 30% compared with total body clearance. Hemodialysis effectiveness is measured by either by hemodialysis clearance, as amount of toxin removed or half-life during hemodialysis (t1/2). Clinical improvement is not a reliable index. Certain agents that predictably cause severe toxicity are routinely dialyzed, based on the blood concentrations or clinical manifestation of toxicity. These include methanol, ethylene glycol, isopropanol, lithium, salicylates (3). Early removal of toxic alcohols prevents toxicity from their toxic metabolites, which are also removed by hemodialysis (4–6). The metabolic acidosis associated with methanol, ethylene glycol, salicylates, metformin poisoning is also corrected during hemodialysis (1,2). High-efficiency and high-flux hemodialysis. Since the 1970s the drive for shorter dialysis time with high urea clearance rates has led to the development of high-efficiency hemodialysis. In the 1990s, certain biocompatible features and the desire to remove amyloidogenic alpha2-microglobulin has led to the popularity of highflux dialysis. These new modalities shorten the time of hemodialysis and have ability to remove middle molecules. During the 1990s, the use of high-efficiency and high-flux membranes has steadily increased. Since initial reports describing their effectiveness in the renal replacement therapy, they have also been used for the treatment of severe poisoning. Several of the published papers there are case-reports in which the effectiveness of these modalities were studied. In acute poisoning with carbamazapine (7–10), phenobarbital (11) and valproic acid (12,13) clinical improvement was observed, the serum drug concentrations were decreased during treatment, dialyzer clearances were higher than those achieved during haemoperfusion. No complications of the procedure were observed. Effectiveness of high-flux hemodialysis in the treatment of life-threatening methanol intoxication also was confirmed (14). Hemofiltration and Continuous Therapies: Hemofiltration achieves solute clearance by convection (or the solvent drag effect) through the membrane, with pore dimensions exceeding those in conventional dialysis membranes, by removing plasma water (which contains dissolved solutes); the removed fluid must be replaced. In hemodiafiltration, diffusive transport is added to hemofiltration to augment the clearance of solutes. Solute clearance is accomplished by circulating dialysate in the dialysate-ultrafiltrate compartment. CAVH is done without a blood pump, the ultrafiltration rate is determined by the positive pressure caused by venous resistance and the negative pressure generated by the height of the drain bag. In CVVH ultrafiltration rate is controlled by a variety of sophisticated machines. All these methods allow continuous removal of small volume of fluid and toxins at low blood flow rates. Also larger molecules up to 50 000 daltons are removed and they are better tolerated in hemodynamically unstable patients. CAVH is mainly useful in intensive care settings in patients with fluid overload. In the treatment of acute poising CVVH and CVVHD, according to the published case reports, effectively removed salicylates in poisoning, (where ongoing absorption from gastrointestinal tract was observed) (15), fluorides, and barium in poisoning with very severe organ toxicity (16,17). In lithium poisoning post-dialysis rebound concentration is the main risk. In such cases CVVH and CVVHD effectively prevent rebound toxicity (18,19). Conclusions: The criteria related to the drugs and chemicals toxicokinetics, the efficacy of the certain dialysis and ultrafiltration techniques and the severity of poisoning should be a guide to their implementation. Clear indices of efficacy need to be defined and agreed for these treatments.