To study the teratogenicity of carbaryl, groups of 10 pregnant mice were dosed, by gavage, with 0, 100, 150 or 200 mg carbaryl/kg body weight, in corn oil, on day 8 or day 12 of pregnancy or daily (as daily doses) from day 6 to day 15. The two higher doses were toxic to both dams and foetuses regardless of the timing of treatment. Treated dams generally showed reduced weight gains but total weight gain was significantly reduced only for dams given 200 mg carbaryl on day 8 or day 12 of gestation. Maternal mortality was increased in most groups given 150 or 200 mg carbaryl. Carbaryl treatment tended to reduce litter size, to increase the percentage of resorbed foetuses, and to reduce foetal weight. There were increased incidences of open eye, of certain visceral abnormalities, and of reduced ossification in virtually all treated groups. The variety of abnormalities in treated foetuses reflected the dysmorphogenic potential of the pesticide. More aberrations were seen in foetuses from dams treated throughout organogenesis than in those from dams given a single dose.