AbstractThe embryolethality of butyl benzyl phthalate (BBP) was studied in Wistar rats. Pregnant rats were given BBP at dosages of 0 (control) and 2.0% in the diet from day 0 to day 20 of pregnancy. Daily intake of BBP was 974 mg kg−1for the 2.0% BBP group. In this group, all dams exhibited complete resorption of all the implanted embryos, and their food consumption, body weight gain and adjusted weight gain (body weight gain excluding the gravid uterus) during pregnancy were markedly lowered. To determine whether the embryolethality was the result of reduced food consumption during pregnancy, a pair‐feeding study was performed in which the pregnant rats received the same amount of diet consumed by the 2.0% BBP‐treated pregnant rats. The pair‐fed and 2.0% BBP‐treated pregnant rats showed significant and comparable reductions in the adjusted weight gain. In the pair‐fed group, the incidences of postimplantation and total losses were higher than those in the control group, and the number of live fetuses per litter was lower than the control value. However, the complete resorption of all the implanted embryos was not found in any of the pair‐fed pregnant rats. It could be concluded that the embryolethality observed in the 2.0% BBP‐treated pregnant rats is attributable to the effects of dietary BBP but not to the maternal malnutrition from reduced food consumption d