The toxicities and skin effects of plasticizers used in rubber and plastic industries were studied in laboratory animals and humans. Twenty five compounds used as plasticizers of synthetic resins were investigated. Rats were administered the compounds by various routes, and mortality was recorded. All animals were necropsied. The compounds were tested for skin irritancy and sensitization in rabbits and humans. Five compounds dioctyl-phthalate (117817), butylbenzyl-phthalate, santicizer-140 (66770443), santicizer-141 (1241947), and flexol-8N8 (61461776) were moderately toxic in doses of 0.6 to 2.4 grams per kilogram (g/kg), generally as a result of intraperitoneal administration. Toxic effects were usually seen in the erythrocytes, blood capillaries, and the central nervous system. The other 20 compounds were essentially nontoxic. All animals supported intraperitoneal injections of 6g/kg or more with no signs of toxic effects. Five compounds showed no skin irritation or sensitization in humans and rabbits: di-2-ethylhexyl-adipate (103231), dibutoxyethyl-diglycol-carbonate, dibutoxyethyl-phthalate (117839), dioctyl-sebacate (122623), and dibutyl-sebacate (109433). Seventeen plasticizers were slight or moderate skin irritants, three were severe skin irritants, and five were moderate sensitizers.