This project is an attempt to show whether the development and progression of the vascular complications of diabetes mellitus are influenced by the type of therapy the diabetic patient receives. It was conceived as a long-term clinical study, partially double- blind, comparing five different treatment programs: 1. Diet plus placebo; 2. Diet plus tolbutamide; 3. Diet plus phenformin; 4. Diet plus a standard dose of Lente Insulin; 5. Diet plus a dose of Lente Insulin required to maintain a 2-hr. postprandial true blood sugar level of 140 100 micrograms. Patients have been subjected to detailed clinical and laboratory evaluation every three months, including fundoscopic photos, creatinine clearance, extremity x-rays, oscillometry, biothesiometry and electrocardiograms, with urinalyses and blood sugar levels obtained at each quarterly examination.