We studied the use of self-monitoring of blood glucose levels and its effect on management in 13 patients with diabetes who were receiving treatment with diet alone, and 53 patients who were receiving oral therapy with hypoglycaemic agents. In the latter group of patients, 40% ceased oral therapy, 17% continued at reduced dosage and 11% at increased dosage, and 11% required insulin therapy. Blood glucose levels improved in virtually all patients. Weight loss occurred in 23 (79%) of the overweight patients. The self-monitoring of blood glucose levels increased motivation and dietary compliance, and allowed the accurate assessment and adjustment of therapy, including the initiation of insulin administration, without the need for an expensive stay in hospital. Self-monitoring is indicated in non-insulin-dependent diabetes mellitus for overweight patients, for the assessment of blood glucose control, for suspected hypoglycaemia in patients taking hypoglycaemic agents, and in patients with an altered renal threshold.