OBJECTIVE To compare the utility of intramuscular lorazepam (LZ) with the combination of intramuscular haloperidol (HDL) and LZ to control acutely agitated behavior. METHODS Randomized double-blind comparison. METHODS Psychiatric emergency service of a large, university-affiliated, municipal hospital. METHODS Twenty subjects treated on the psychiatric emergency service. METHODS Patients received an injection of either LZ 2 mg (11 patients) or HDL 5 mg plus LZ 2 mg (9 patients). The Overt Aggression Scale (OAS), visual analog scales reflecting agitation and hostility, and the Clinical Global Impressions (CGI) severity scale were administered at baseline and 30, 60, 120, and 180 minutes after the injection. RESULTS Planned data comparisons included categoric assignment of patients as improved, as defined by decreases in outcome measures 60 minutes after the injection, as well as continuous variables up to 180 minutes after the injection. A significantly greater percentage of subjects receiving combined treatment improved on the specific measures 60 minutes after dosing (p<0.05). Kaplan-Meier survival analyses showed significant between-group differences in survival curves plotted for the entire study period (p<0.05). Repeated measures analyses of variance studying group differences showed that both groups improved over time, but between-group differences were not significant. The powers of these analyses were low due to the small sample. No serious adverse effects occurred in either treatment group. CONCLUSIONS Our results suggest superior efficacy for HDL-LZ over LZ alone. Categoric tests of improvement at 60 minutes provided the strongest evidence of group differences.