Adult pregnant female rats were exposed to subchronic doses of parathion throughout gestation and lactation. Their offspring were examined for possible toxicological effects. This study found that several physiological parameters were affected. Female perinates exhibited a significant reduction in plasma cholinesterase (pseudo ChE) activity. Plasma renin activity was reduced with increased dose of parathion in both male and female perinates. Heart rate, QRS complex duration, S-T and P-R intervals were all reduced in the perinates. The results of this study indicated that physiological function can be altered by organophosphate exposure at levels lower than those required to show pseudo ChE inhibition.