The effects of three pharmacological treatments, methylphenidate hydrochloride, thioridazine hydrochloride, a methylphenidate/thioridazine combination, and placebo were studied in outpatient hyperkinetic children rated hyperactive both in school and at home or clinic. Active treatment lasted 12 weeks; placebo lasted four weeks. Significant clinical improvement was obtained in a variety of settings--all treatments were superior to placebo on ratings filled out by parents, teachers, and clinic staff. Though initially the combination of methylphenidate and thioridazine tended to produce greater clinical improvement, it was not superior to methylphenidate alone after 12 weeks of treatment. Methylphenidate alone and the methylphenidate/thioridazine combination were more effective than thioridazine alone. The salient side effects with methylphenidate treatment were decrease in appetite, difficulty in falling asleep, and increased mood sensitivity. In contrast, thioridazine administration was associated with appetite increase and enuresis.