The effect of a consultant pharmacist on medication use in an institution for the mentally retarded was studied. One year after hiring the consultant pharmacist and the implementation of a multidisciplinary approach to patient care at institution A, a previous medication survey was repeated for 715 patients. Medication use at a nearby mental retardation institution (institution B) with 1049 patients was surveyed once. The overall percentage of patients receiving antipsychotics or anticonvulsants in institution A was not different in the two surveys. There was a significant increase in the percent of patients receiving single drug entities in the second survey (for antipsychotics, 4.9% versus 9.1%; for anticonvulsants, 2.7% versus 15.1%). The use of long-term medications decreased from 76.1% to 56.8% of the population, and the use of individual antipsychotic agents changed significantly. The survey at institution B, a similar facility with less direct pharmacy involvement, showed significantly more use of antipsychotics than at institution A (34.2% versus 16.8%) and fewer patients receiving no long-term medications (29.2% versus 43.2%). The results suggest that the direct clinical involvement of skilled pharmacists in cooperation with other health professionals can significantly alter the patterns of medication use in a long-term care facility for the mentally retarded.