An accurate pattern of blood-glucose changes in everyday life is the basis for treatment in insulin-dependent diabetes. 69 patients were taught to obtain their own blood-glucose profiles with a 'Reflomat' Boehringer Mannheim) reflectance meter on one working and one rest day, and to repeat these where necessary after adjustment of treatment. 2 did not complete the study satisfactorily. The other 67 produced profiles on 241 dyas. Even patients with a limited education could use the technique accurately and their readings correlated closely with simultaneous laboratory values (r = 0.96). Self-monitoring was especially useful in elucidating problems in diabetic control, preventing hypoglycaemia, and managing diabetic pregnancy. Unlike the measurement of HbA1c which only detects poor diabetic control, self-monitoring also shows how to improve it. Patients found self-monitoring more informative than urine tests; their active involvement in management of their disease resulted in better motivation, greater understanding of diabetes, and a sustained improvement in control. By the end of the study 32 of the 67 patients ahd profiles in which no more than one blood-glucose value exceeded 10 mmol/l. Smaller and more portable machines will make the technique more widely applicable.