Azamethiphos (CAS No. 35575-96-3) was evaluated for developmental toxicity. Twenty-nine, 24, 22, and 24 pregnant Sprague-Dawley rats were treated with 0, 25, 75, and 150 mg/kg/day of the test material, respectively, by oral gavage on days 6-15 of gestation. Feed intake was reduced in the 150 mg/kg/day dose group. Body weight gain was unaffected by treatment. Rates of implantations, embryolethality (resorptions), and average weights of the fetuses were comparable to controls. An increased number of not yet ossified calcanei and phalangeal nuclei of hind-limb was observed at 150 mg/kg/day. These effects were related to the toxic effects on the dams. At 25 and 75 mg/kg/day no treatment- related effects were observed. No teratogenic effects were observed at any treatment level.