1. 1. Clinical variables determining length of psychiatric hospitalization for psychotic inpatients were explored. Forty psychotic inpatients received a 14 day fixed dose neuroleptic trial. 2. 2. Neuroleptic responders ( 25 40 ) were discharged 15 ± 2 days after initiation of phannacotherapy. For neuroleptic non-responders ( 15 40 ) antipsychotic medication was then altered as clinically indicated. Patients requiring one change in medication (N = 8) were discharged after 27 ± 5 days; those requiring two medication adjustments (N = 4) were discharged after 33 ± 3 days and those requiring three alterations in phannacotherapy (N = 3) were discharged after 42 ± 12 days. 3. 3. Statistical analysis of clinical and diagnostic variables indicated that 84% of the variation in length of hospitalization was accounted for by the number of alterations in phannacotherapy required for symptom remission and discharge. It is suggested that length of hospitalization may be decreased by decreasing the length of time a clinician prescribes phannacotherapy that subsequently proves not effective. 4. 4. Bayesian analysis was employed to identify the minimum length of pharmacotherapy which accurately predicts subsequent antipsychotic response/non-response. During the fixed dose neuroleptic trial response/non-response could be accurately predicted for 65% of the patients by Day 3 of the trial while by Day 7 response/non-response could be predicted for 80% of the patients. 5. 5. The present data indicate that a three to seven day trial of antipsychotics may be sufficient for making phannacotherapy decisions as such a trial demonstrates a diagnostic efficiency similar to other predictive tests employed in clinical medicine.