Desmopressin and ethamsylate were evaluated for possible synergistic effects on the bleeding time. The drugs were administered individually and together to 12 patients with markedly prolonged bleeding times known to be relatively or absolutely unresponsive to desmopressin alone. The bleeding disorders studied included Glanzmann's thrombasthenia (one), other disorders of platelet function (four), pseudo-von Willebrand disease (one), and von Willebrand disease type I (three), type II (two), and type III (one). Desmopressin alone shortened the bleeding time from 23.9 +/- 1.5 to 19.5 +/- 2.3 min (p = 0.03). Ethamsylate alone was without effect. Desmopressin and ethamsylate together shortened the bleeding time to 11.2 +/- 1.4 min (p less than 0.01 compared to baseline, p = 0.02 compared to desmopressin alone). The combination was ineffective in three patients, with Glanzmann's thrombasthenia (one), and von Willebrand disease type I (one) and type III (one). Toxic effects of the drugs were not observed. Five patients received desmopressin and ethamsylate prior to dental work with mandibular block (one), heart surgery requiring cardiopulmonary bypass (two), and adenotonsillectomy surgery (two). Normal hemostasis was achieved in each case. A synergistic shortening of the bleeding time was observed with the combination of desmopressin and ethamsylate in a wide range of bleeding disorders.