Technical xylene (cas. nr. 1330-20-7) was investigated for development toxicity in a teratology and in a postnatal study. Rats (Mol: WIST) were exposed to 500 p.p.m. 6 hr per day on days 4 to 20 of gestation. There were no signs of maternal toxicity. In the teratology study, no exposure-related differences were found except for delayed ossification of os maxillare. In the postnatal study, the xylene-exposed pups had a higher body weight and an impaired performance on a motor ability test (Rotarod). Due to the possibility of direct toxic effects of xylene on the developing central nervous system, further studies are needed to investigate dose-effect relationship for this type of effects.