Administration of the tricyclic dibenzazepine drug imipramine, a tertiary amine, in the food (100 mg/kg) or sodium nitrite (1 g/liter) or dimethylnitrosamine (0.1 ppm) in the drinking water of Swiss CD-1 mice before and during pregnancy, resulted in increased perinatal death of the offspring compared to controls. Administration of imipramine and nitrite together had no effect on perinatal survival, but instead resulted in infertility or delayed impregnation in some females. A biological synergism or in vivo chemical interaction of the two chemicals is suggested.