Recent research on the toxicology of formaldehyde (50000) was reviewed. Formaldehyde and phenolic formaldehyde resins widely used in industry have been shown to be strong contact sensitizers. Formaldehyde in dilute solutions used to preserve tissues in pathology laboratories can diffuse through protective gloves; however, systemic absorption has not been observed to occur by this route. The risk posed by exposure to formaldehyde outgassing from urea-formaldehyde and phenol-formaldehyde insulation in mobile homes was mentioned. Occupational asthma has been a common complaint of workers exposed to formaldehyde; however, low formaldehyde concentrations, 0.1 to 3 parts per million (ppm) did not induce bronchoconstriction in patients under laboratory conditions, although higher concentrations did. Formaldehyde has been shown to inhibit repair of nucleic acids, to potentiate the effects of alkylating agents, and to induce unscheduled DNA synthesis and chromosome aberrations in human tissues. Methods for monitoring exposure to formaldehyde were discussed. Formaldehyde carcinogenicity was discussed. Formaldehyde vapor induces nasopharyngeal carcinomas in rats at concentrations comparable to those measured in some workplaces. The dose response is not linear. For example, formaldehyde induced nasopharyngeal carcinomas in 50 percent of the rats exposed to 14.3ppm, but in only 1 percent of those exposed to 5.6ppm. No tumors were seen in rats exposed to 2ppm formaldehyde. Epidemiological studies have shown an increased risk of lymphatic, lung, or prostate cancer, but not nasal cancer, in exposed populations. Retrospective studies using tumor registries, however, have found an association between nasal cancer and a history of formaldehyde exposure. The new OSHA standards for formaldehyde were discussed. The new standard is 1ppm for an 8 hour time weighted average (TWA) exposure, with a 2ppm maximum peak exposure for a 15 minute sustained time exposure limit. An 8 hour TWA exposure of 0.5ppm is the action level. The author concludes that recent data suggest strongly that formaldehyde should be regarded as a potential human carcinogen.