Plasma prolactin (PRL) and homovanillic acid (HVA) levels, and urinary HVA and dopamine (DA) excretion, were measured in groups of unmedicated autistics, medicated autistics, and normal controls. No significant differences were found between unmedicated autistics and normal controls in plasma PRL and HVA levels. Excretion rates of urinary HVA and DA were also similar in the unmedicated autistic and normal subjects. Plasma PRL and HVA, as well as urinary HVA excretion, were significantly increased in the autistics on neuroleptic medication compared to the unmedicated autistics. A significant correlation (r=0.46, p =<0.05) was observed between dose of neuroleptics and plasma PRL values; the correlation (r=0.42) between neuroleptic dose and plasma HVA levels approached significance (p=0.06). In contrast, no differences were observed in urinary DA excretion between medicated and unmedicated autistics. In general, the findings indicate that peripheral indices of dopamine functioning are normal in autistic subjects.