22 patients complaining of primary menorrhagia or menorrhagia associated with an intrauterine device (I.U.C.D.) were studied in a double blind trial with crossover of ethamsylate and placebo. Acutal menstrual blood-losses were calculated from the iron content of used sanitary material during one pre-trail menstrual period and four trial menstrual periods, during which patients received ethamsylate ("Dicynene") treatment during two menstrual cycles and placebo during two cycles. During ethamsylate treatment the mean menstrual blood-loss was reduced by 50% in patients with primary menorrhagia and by 19% in patients with an I.U.C.D. This difference between the two groups is probably accounted for by the differing values of initial blood-loss which was significantly higher in the group with primary menorrhagia. Tampon usage and the duration of bleeding were not significantly altered by ethamsylate treatment. Reported side-effects, which were not serious, were equally common during ethamsylate and placebo treatment.