The effects of PBB on 33 children born between September 1, 1973, and December 31, 1975, were evaluated in September, 1977. These children, born to families who lived on quarantined farms, were compared to 20 children who were not exposed to PBB. The birthdate interval was selected to obtain children who were exposed in utero or in early infancy or both, the two time periods when damage to developing tissues and organ systems should have been maximal. The results of these studies failed to identify any effects on physical growth, physical examination, or neurologic assessment, although the parents indicated by historical review that the exposed children had had more illnesses, especially respiratory, than had the control children. There were some indications of an inverse relationship between PBB fast level and performance on selected developmental tests.