The effects of gabexate mesilate on disseminated intravascular coagulation (DIC) accompanying neoplastic diseases or severe infections in ten patients were investigated and compared with those of heparin therapy in ten other patients with DIC. Of 11 patients with DIC (control) who did not receive any anticoagulation therapy for DIC, ten died of pneumonia, DIC secondary to the underlying diseases, or pulmonary edema. Heparin therapy was effective in five patients (50%), while treatment with gabexate was successful in seven patients (70%). Although the therapeutic efficacy of gabexate was not significantly different from that of heparin, in patients in whom bleeding tendencies were observed at the start of the therapy, the former was successful in four (80%) of five patients, while the latter was effective in only one (25%) of four patients treated. The results of this preliminary and nonrandomized study suggest that gabexate is as effective as heparin for the treatment of DIC, and that it may be more successful than heparin in the treatment of DIC accompanied by bleeding diathesis.