Baygon and Carbofuran were administered to CD rats on the 7th through 19th day of gestation, while dimethoate and EPN were administered to CD-1 mice on the 6th through 16th day of gestation. Baygon did not produce fetotoxicity, nor was it found to be teratogenic. Increased fetal mortality and decreased fetal weight occurred at maternally lethal doses. Carbofuran was not teratogenic but was found to be fetotoxic at higher dose levels. Dimethoate was not teratogenic but depressed maternal weight gain at lower doses and increased maternal lethality at higher dose levels. EPN administered at maternally lethal doses did not produce fetotoxicity, fetal lethality or an increase in malformations. These few studies with baygon, carbofuran, EPN and dimethoate in the mammalian fetus indicated the need for teratology studies with these pesticides.