Lipid metabolism, platelet function, and blood coagulability were evaluated in 20 patients with diabetes mellitus and stable fasting blood sugar levels before, during, and after treatment with the pancreatic enzyme elastase for 16 weeks. Serum high-density lipoprotein cholesterol levels increased from 46.9 mg/dl before treatment to 53.2 mg/dl after treatment (P less than 0.001) and serum triglyceride levels decreased from 151.4 to 125.4 mg/dl (P less than 0.05); no significant changes in total cholesterol levels were noted. Platelet counts in whole blood and in platelet-rich plasma increased from 17.1 and 27.5 X 10(4)/mm3, respectively, to 19.8 and 31.3 X 10(4)/mm3 after treatment (P less than 0.01 and less than 0.05). Plasma beta-thromboglobulin levels decreased from 117.0 to 72.7 ng/ml after treatment (P less than 0.001). No significant changes in platelet sensitivity to adenosine diphosphate aggregation were noted. Plasma fibrinogen and antithrombin III levels increased from 421.0 and 25.8 mg/dl, respectively, to 470.6 and 32.0 mg/dl after treatment (P less than 0.05 and less than 0.001). It is concluded that, since it has been shown that elastase improved lipid metabolism, inhibited platelet release, and increased antithrombin III levels, it may play a useful role in the prevention of vascular complications in diabetic patients.