Bar-code technology was used to determine: (1) patterns in histamine H2-receptor antagonist use and (2) the occurrence of adverse drug effects and drug interactions associated with the use of these agents in critically ill patients. Patients at Henry Ford Hospital (Detroit) receiving histamine H2-receptor antagonists over a two-month period were evaluated. Clinical information was collected in the intensive care units by using a bar-code system. The data-capture menu was based on drug-use-evaluation criteria for H2-receptor antagonists. Data collected in the scanning wands were uploaded into a computer database and were analyzed at the end of the study. Data were collected for 207 patients. Cimetidine was the predominant H2-receptor antagonist used, and the predominant indication was stress-ulcer prophylaxis. Dosing trends followed accepted guidelines for cimetidine dosage adjustment in renal and hepatic failure. Two drug interactions and six adverse drug reactions occurred. Pharmacists made 92 recommendations to the medical staff regarding modification in therapy, involving 32% of the patients. Data collection required an average of 10 minutes per day each for three pharmacists. H2-receptor antagonist use patterns were evaluated in intensive care units through the application of bar-code technology. The speed and efficiency of this automated tool facilitated collection of a large amount of data.