In this 30-hospital survey, data on usage, adverse drug reaction (ADR) rates, and drug interactions (DI) of the H2-receptor antagonists (H2RA) cimetidine, ranitidine, and famotidine were analyzed. Approximately 8% (1,768 patients) admitted to participating hospitals received an H2RA (range: 0.5 to 30%). Patients admitted to a critical care area were significantly (p less than 0.025) more likely to receive ranitidine, were more likely (p less than 0.005) to receive more than one H2RA, and were more likely (p less than 0.0005) to receive an H2RA for "stress ulcer" or a "history of peptic ulcer disease". Doses of the H2RAs were appropriate in less than 50% of cases. Sixty ADRs and 29 DIs were reported. There was no significant difference (p greater than 0.70) between cimetidine and ranitidine with regard to the number of ADRs reported; however, cimetidine was associated with a significantly greater (p less than 0.0005) number of reported DIs. The results of this utilization review indicate that H2RAs are frequently prescribed drugs in hospitalized patients. All ADRs and DIs were reported in patients in critical care areas, suggesting that these patients are "at risk" of developing side effects to H2RAs.