In an ongoing effort to delineate structure-activity relationships in the developmental toxicity of diphenyl ethers, we evaluated the maternal and developmental toxicity of 10 diphenyl ethers related to the herbicide nitrofen. All possible trichlorophenyl 4Π-nitrophenyl ethers were evaluated, as were the 2,4-difluorophenyl and 2,4-dibromophenyl 4Π-nitrophenyl ethers. We also evaluated bifenox and chlomethoxyfen, which are 2,4-dichlorophenyl congeners with metasubstituents on the 4Π-nitrophenyl ring. Nitrofen (2,4dichlorophenyl 4Π-nitrophenyl ether) was included for comparison. Identity of the halogen affected the postnatal (but not prenatal) mortality induced by 2,4-dihalogenated 4Π-nitrophenyl ethers. The presence of 3Πsubstituents on the 4Π-nitrophenyl ring reduced both pre-and postnatal toxicity of 2,4-dichlorinated congeners. Among chlorinated 4Π-nitrophenyl congeners without meta-substituents on the nitrophenyl ring, the position of chlorine substituents strongly affected the congener's potential for inducing prenatal vs. postnatal syndromes. All congeners increased liver to body weight ratios in unmated females, but such increases were not well-correlated with either prenatal or postnatal embryotoxicity.