We report our first experience with a new microprocessor device for assisting individuals with diabetes in the adjustment of insulin therapy. The computer weighs 200 g and can receive, store, and analyze patient-entered capillary blood glucose (CBG) data on an ongoing basis. Changes in the injected mixtures of short- and intermediate-acting insulins are recommended according to algorithms designed to bring the premeal CBG levels to any desired target value set by the physician. Throughout the present study, the premeal target glucose level was set to 110 mg/dl. Seven (type I) insulin-dependent diabetic individuals ranging in age from 11 to 43 yr were selected to participate in the first use of a BCMC (Better Control Medical Computers, Inc., Toronto, Ontario, Canada) computer on an outpatient basis. All subjects were concerned about diabetes control and were fully informed about as well as thoroughly practiced in the use of manual insulin dosage adjustment schemes, based on approximately equal to 4 times daily CBG estimation, as currently taught in our diabetes clinics. During the last 7 days of the control period of self-adjustment, their mean +/- SEM CBG levels (measured before breakfast, lunch, dinner, and bedtime snack) were, respectively, 178 +/- 20, 187 +/- 35, 208 +/- 22, and 207 +/- 13 mg/dl. Immediately after the control period they were given the device and were instructed in the procedure for entering glycemic data and following manufacturer's recommendations in regard to insulin dosages. This experimental period lasted 8 wk and the outcome was assessed as before. Thus, 8 wk after starting daily use of the instrument, all glycemic values measured as before had fallen significantly (P less than 0.005-0.05) closer to normal: 116 +/- 9, 110 +/- 6, 148 +/- 15, and 135 +/- 9 mg/dl, respectively. Concurrently there was also a significant (P less than 0.01) reduction in the variability of glycemia measured before the main meals.(ABSTRACT TRUNCATED AT 250 WORDS)