Ten patients with schizophrenia participated in 120-min free-smoking sessions when actively psychotic and free of antipsychotic medications, and again after the initiation of haloperidol treatment. During these free-smoking sessions they had access to cigarettes ad libitum. Their expired air carbon monoxide (CO) and plasma nicotine and cotinine levels were measured at the end of the 120-min free-smoking sessions. These patients smoked more after starting haloperidol treatment, relative to their baseline rate of smoking when free of antipsychotic medications, as evidenced by significantly higher expired CO and plasma nicotine levels.