Fifty-five women with primary dysmenorrhea were enrolled in a study which each took ibuprofen (400 mg), propoxyphene hydrochloride (64 mg), or a placebo alternately in consecutive menstrual cycles for relief of pain. Fifty-one completed the study during three successive cycles in this triple-blind, crossover, randomized investigation. Ibuprofen was clearly superior to propoxyphene and the placebo in patient preference, degree of relief, and need for supplementary analgesics. In addition, a significantly greater number of patients were able to pursue their normal daily functions during the ibuprofen cycle. Propoxyphene was superior to the placebo but not to the same extent as ibuprofen. Only three side effects were reported during the study, two relative to propoxyphene and one recorded during a placebo cycle. These data show that ibuprofen is an effective agent when used for treatment of dysmenorrhea without organic etiology.