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 4'-nitrophenyl ethers were evaluated, as were the 2,4-difluorophenyl and 2,4-dibromophenyl 4'-nitrophenyl ethers. We also evaluated bifenox and chlomethoxyfen, which are 2,4-dichlorophenyl congeners with meta-substituents on the 4'-nitrophenyl ring. Nitrofen (2,4-dichlorophenyl 4'-nitrophenyl ether) was included for comparison. Identity of the halogen affected the postnatal (but not prenatal) mortality induced by 2,4-dihalogenated 4'-nitrophenyl ethers. The presence of 3'-substituents on the 4'-nitrophenyl ring reduced both pre- and postnatal toxicity of 2,4-dichlorinated congeners. Among chlorinated 4'-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.