Thioridazine and visual screening procedures are effective in reducing the stereotypic behaviors of individuals with mental retardation. A double-blind, placebo-controlled study, using alternating treatments within a multiple-baseline across subjects design, was conducted to assess the effects of two doses of thioridazine (1.25 and 2.5 mg/kg/day) and visual screening, alone and combined, on stereotypy and social behavior of three individuals with profound mental retardation. Functional analyses did not show demand, alone, social attention, or differential reinforcement conditions to maintain the subjects' stereotypy. Thioridazine was effective in producing modest reductions in stereotypy and minor increases in social behavior across subjects. The higher dose of thioridazine (2.5 mg/kg/day) was slightly more effective than the lower dose (1.25 mg/kg/day), and thioridazine plus visual screening was more effective than thioridazine alone. The most effective treatment was visual screening when used in the absence of thioridazine. This study demonstrates a method for assessing the impact of psychopharmacological and behavioral interventions in individuals for whom a behavioral treatment cannot be easily derived from a functional analysis of the maintaining conditions of the target behavior.