The phase II/III U.S. clinical drug trials for cimetidine (Tagamet) in duodenal ulcer were examined for their potential application to cost-benefit analysis. Data on "time lost from work" were obtained from a special protocol added to these short-term, double-blind trials of cimetidine. Sixty-four outpatients from the clinical trials remained from an original pool of 217 after exclusion of those subjects who were either retired, unemployed, or of uncertain employment status. Cimetidine was significantly more effective than placebo in reducing "time lost from work" during ulcer disease. The patients' "time lost from work" occurred as a strikingly all-or-nothing phenomenon. We conclude that a prospective clinical trial is appropriate for gathering economic data.