The OECD421 reproductive toxicity screening test protocol was evaluated using the reproductive and developmental toxicant butyl benzyl phthalate (BBP). Female rats were orally exposed from 14 days premating to 6 days postpartum. Male rats were exposed for 29 days. At 1000 mg/kg bw/day effects were found on body weight gain and food consumption, on spermatogenesis, time to conception, pregnancy rate, postimplantation survival, and litter size and weight. Food consumption and pup weight were slightly affected at 500 mg/kg also. Effects occurred at expected dosages on the basis of literature data. These findings support the conclusion that the OECD421 test scores BBP correctly as a reproductive toxicant, both in a qualitative and in a quantitative sense.