The design of the study was "2-period changeover"; each period lasted 6 months and 6 counseling sessions were offered during each period. Group 1 (n = 81), counseled in the first period, was controlled by a noncounseled group 2 (n = 82). Randomization of patients into the 2 groups took place at each office. The primary variable for consideration was the postprandial (pp) blood sugar level (mg/dl). Weight reduction of overweight patients was also considered. A highly significant (p less than 0,01) difference of mean pp-blood sugar reduction between the groups was found during both periods. In view of the large estimated difference in the residual effects of both treatments (counseling, no counseling) a crossover analysis was excluded. The best pp-blood sugar effect was obtained for patients with high pp-blood sugar level (greater than or equal to 250) at the beginning of the counseling period.