An analysis is presented of data collected to evaluate the impact of a clinical pharmacy service on an acute psychiatric admitting unit. Retrospective longitudinal drug utilization reviews (RLDUR) were performed one year apart (pre- and post-implementation of services) on the same treatment team. Process measures significantly affected include (percent reduction): total drugs/patient (33.9), number of antipsychotic drugs/patient (38.0), number of anticholinergic started on admission/patient (53.2), and number of doses/patient/d (42.4). Other drug-use parameters significantly affected include: a 42-percent increase in the mean dosage expressed as chlorpromazine equivalents, and a 47-percent reduction in the number of patients on low potency antipsychotic medications. Beneficial outcome was reflected by a faster rate of discharge or transfer to a less restrictive ward environment in the pharmacy study population. The study population also demonstrated a 55.8-percent decrease in their readmission rate to the facility over a one-year follow-up period. Clinical pharmacy services positively affect both process and outcome health care measures.