Actively psychotic schizophrenic and nonpsychotic psychiatric inpatients received intravenous methylphenidate hydrochlroide (0.5 mg/kg). Each patient was rated for level of psychosis and talkativeness, and each received the Holtzman projective ink blot tests and the Kent-Rosanoff word-association tests before, during, and after methylphenidate infusion. Minnesota Multiphasic Personality Inventory Goldberg Index scores were also obtained as a general measure of psychosis. For the entire patient group, methylphenidate infusion was followed by a significant increase in talkativeness and psychosis ratings and in pathological responses to the Holtzman ink blot test. There was a significant decrease in common word associations. Since neither of the psychological tests allow more than one response per item, it appears that methylphenidate truly effects pathological thought processes and decreases common word associations as such, rather than merely making these processes more evident by increasing verbalization.