Pregnant Wistar rats were treated with different concentrations of toluene by inhalation (300, 600, 1000 and 1200 ppm) from day 9 to day 21 of pregnancy for 6 h a day in a whole-body inhalation chamber (controls inhaled fresh air only). From day 22, rats were kept single-caged and were allowed to deliver. Besides a detailed evaluation of the physical development of the offspring we performed the following tests: forelimb-grasp reflex, righting reflex, cliff-drop aversion reflex, maintainance of balance on a rotating rod, measurement of locomotor activity and learning ability in a discrimination learning test. A toluene exposure of 1200 ppm resulted in a reduced body weight of rat dams and offspring and a higher mortality until weaning. The physical development (incisor eruption, eye opening and vaginal opening) was retarded in this group. There were no clear-cut and concentration-dependent differences in the development of reflexes, rota rod performance and locomotor activity between the offspring of animals exposed to toluene and the controls. Likewise, no effects were found on learning ability in the operant conditioning task. Compared to the controls there were no differences in mating, fertility and pregnancy indexes in the F1-generation. The tests performed have provided no evidence that toluene exposures < or = 1200 ppm induce adverse effects on the behaviour of rat offspring exposed during late embryonic and fetal development.