All 11 maturity-onset diabetics (age 55 to 79 years) switched from oral hypoglycemics to insulin during one year in our department, even though metabolically stable, have been followed up. The main reason for the change was a diminished sense of well-being combined with relatively ill-defined symptoms such as declining physical performance, fatigue, dizziness and pain in the legs. None of the patients was ketoacidotic and the 24-hour glucosuria was less than 15 g, although the average fasting blood sugar was markedly elevated to 296 mg/dl. After 6 months on insulin the 24-hour glucosuria had not changed but the fasting blood sugar had dropped to 183 mg/dl. This was accompanied by an improved sense of well-being (as measured by an analog scale) and by disappearance of the symptoms mentioned above. Even though 9 of the 11 patients were initially reluctant to change to insulin, all 11 were still on this drug after 6 months. The authors recommend broadening the indications for insulin therapy in stable adult-onset diabetics, particular attention being paid to vague symptoms such as fatigue and decreased physical performance.