The objective of the investigation was to evaluate the effect of metformin added to the usual insulin treatment on insulin resistance, on the dose of substituted insulin and on the compensation of type 1 diabetes. Method: The first part of the study lasted 3 months, it was an open prospective study. The group was formed by 22 type 1 diabetics ,average age 38.9 ± 8.93 (min. 21, max. 55), with duration of diabetes of 13.8 ± 6.43 years (min. 4, max. 29). Insulin resistance was assessed by means of a hyperinsular euglycaemic clamp (insulinaemia 100 mlU/l) at the onset of the study (B), after three months of metformin treatment which was added to the insulin regimen in a dose of 2 x 850 mg (M). After the same intervals the other investigasted parameters were assessed (body weight, daily insulin dose, glycated haemoglobin, triacylglycerols and cholesterol). The second part of the study was implemented after three years in the same group. The check-up examination (K) was attended by 21 diabetics who were divided into two groups: those who steadily used combined treatment (X,8 patients) or were treated only with insulin (Y, 13 patients). The authors followed up the development of metabolic parameters in groups X and Y and the differences between them. Results: After three months combined treatment reduction of body weight was recorded, on average by 2.23 kg (by 2.9 %, p < 0.001) and reduction of the daily insulin dose on average by 12.7 IU ( by 20 % , p < 0.001).The decline of insulin resistance and glycated haemoglobin did not reach statistical significance. The lipaemia levels did not change. After three years the positive effect of combined treatment (group X vs. Y) wss preserved only as regards maintenance of body weight (p < 0.005). Conclusion:After adding metformin to the insulin regimen of type 2 diabetics after three months a statistically significant drop of body weight and the daily insulin dose occurred. Glycated haemoglobin and resistzance declined insignificantly. After follow up of the combined regime three years later only a positive effect on maintensance of the reduced body weight was recorded in group X vs. Y (p < 0.05).the other parameters in both groups did not differ statistically after three years.

        Key words: Diabetes melitus - Insulin resistance - Therapy - Metformin