LD sub 50 values were determined for 57 pesticides administered by the oral or dermal route to adult male and female Sherman rats. Nine pesticides tested by the oral route (bufencarb, cacodylic acid, dialifor, deltamethrin, dicamba, diquat, quintozene, phoxim, pyrazon) and 4 tested by the dermal route (bufencarb, chlordimeform, dichlofenthion, leptophos) were more toxic to females than to males whereas famphur and 2,4,5-T (oral route) were less toxic to females. Eighteen of the test chemicals were more toxic to the adult than to the weanling and 4 compounds (leptophos, methidathion, pyrazon and sulfoxide) were more toxic to the weanling. In additional studies the variability of the LD sub 50 value over a one year period was examined for 2 typical insecticides. Six consecutive bimonthly oral LD sub 50 determinations for parathion and DDT in adults of both sexes indicated that the LD sub 50 values were little affected by the time of year that the tests were done.