Dibutyl phthalate, a plasticizer, is a teratogen in mice and rabbits but produces fetal loss in the rat. Long-term dosing studies indicating reduced fertility in the rat suggested a maternal effect of the compound. The decidual cell response (DCR) and pregnant rats were used to examine whether DBP affects maternal physiological parameters independent of the compound's fetotoxic effect. DBP has no effect on the DCR, pregnant uterine weight, number of implantation sites, ovarian weight, or serum progesterone concentration during early pregnancy or pseudopregnancy. These data show that short term dosing with DBP has no direct maternal effect in the rat and suggest that the viability of preimplantation embryos is not compromised.