The efficacy of a benzodiazepine was compared with that of a neuroleptic for the rapid tranquilization of patients presenting at a psychiatric emergency room service. Thirty-seven highly agitated patients exhibiting psychotic symptoms were randomly assigned to receive either 2 mg lorazepam or 5 mg haloperidol as needed every 30 min for 4 h. Administration route was either intramuscular injection or oral concentrate. Symptom ratings were conducted each hour using double-blind procedures. Both medications reduced symptom ratings on the Brief Psychiatric Rating Scale and Global Clinical Impression of Overall Symptom Severity Scale. Global Clinical Impression scores for the two medication groups did not differ significantly either at baseline or at 4 h after entry into the study. However, Global Clinical Impression scores of patients in the lorazepam group were less severe at intermittent ratings. The groups did not differ on the Brief Psychiatric Rating Scale at any rating time. No differences were found either in the number of doses administered or in the administration route selected. Given the potential for severe extrapyramidal symptoms developing hours or days after a single dose of haloperidol, lorazepam may provide an excellent alternative for the rapid tranquilization of the acutely agitated psychotic patient in the emergency room setting.