The purpose of this study was to evaluate the teratogenic potential of the propylene glycol butyl ether (PGBE) and isooctyl (IO) esters of 2,4-dichlorophenoxyacetic acid (2,4-D). Accordingly, groups of pregnant CD rats received daily oral doses of PGBE or IO equivalent to 0, 6.25, 12.5, 25.0, or 87.5 mg/kg/day of 2,4-D from day 6 through day 15 of gestation, and fetuses were observed for gross, soft tissue, and skeletal defects. In addition, a postnatal study was performed on rats receiving 0, 12.5, or 87.5 ME/kg/day PGBE or IO to determine the effect of treatment on growth and survival of pups. No adverse effects were observed on maternal welfare, nor was there any evidence of embryo or fetal lethality in any of the treated groups. Of the anomalies observed, the incidence of lumbar (14th) rib buds was found to be statistically increased in the groups given the 87.5 mg/kg/day doses of both PGBE and IO. No other anomaly reached a level of statistical or toxicological significance. The number of pups per litter was significantly reduced on postpartum days 4 and 7 in dams receiving 87.5 ME/kg/day IO. However, mean pup body weight remained normal. Postnatal growth and survival of pups receiving PGBE were not adversely affected. It was concluded that PGBE and IO caused minor embryotoxicity which was not deleterious to growth and survival, and therefore was not teratogenic to offspring of treated rats.