The developmental and behavioral toxicity of gestational exposure to low levels of cadmium (Cd, 4.2 and 8.4 micrograms/ml in drinking water) were assessed in rats. Significant decreases in birth weight and growth rate were observed in the 8.4 micrograms Cd/ml group. The metal exposure had no effect on the ontogeny of physical landmarks, surface and air righting reflexes and visual placing, but a significant hyperactivity and delay in the development of cliff aversion and swimming behavior were observed in the neonatal pups of either treatment group. Marked decreases in the locomotor activity shuttle box performance were evident at 60 days but not at 90 days of postnatal life. The apomorphine-induced hyperactivity was not affected in these rats at either age. These data indicate that Cd exposure during the critical periods of development might result in developmental and behavioral deficits with longterm implications on adult behavior.