The low calorie juice Aronia melanocarpa (sugar free, with artificial sweeteners) could be a valuable adjunct to the complex therapy of patients with diabetes mellitus. In this study no increased blood glucose levels were established 60 min. following ingestion of 200 ml Aronia juice. On the contrary, lower fasting blood glucose concentrations were measured in 16 patients with insulin dependent diabetes and in 25 patients with non-insulin dependent diabetes (25 women and 16 men, 3 to 62 years of age, median age 38.8 +/- 4.7) with duration of the disease from 1 month to 13 years. Serial blood glucose measurements showed: 14.23 +/- 1.32 mmol/l at baseline and 11.4 +/- 0.89 mmol/l blood glucose level after 60 min., the difference being statistically significant (p<0.05). The ingestion of 200 ml Aronia juice combined with a standard breakfast produced similar results (the basal concentration of glucose was 13.43 +/- 1.12 mmol/l; it decreased to 11.94 +/- 1.02 mmol/l at 60 min., the difference did not reach statistical significance. The daily intake of 200 ml Aronia juice over a period of 3 months was effective in lowering fasting blood glucose levels from 13.28 +/- 4.55 mmol/l to 9.10 +/- 3.05 mmol/l (p<0.001) in 21 patients with non-insulin dependent diabetes--13 women and 8 men aged from 42 to 62 (median age 53.6 +/- 3.65) with disease duration from 6 to 17 years. Aronia had a beneficial effect on HbA1c, total cholesterol and lipid levels. They dropped from 9.39 +/- 2.16% to 7.49 +/- 1.33% (p<0.001), from 6.45 +/- 1.59 mmol/l to 5.05 +/- 0.96 mmol/l (p<0.001) and from 2.92 +/- 2.15 mmol/l to 1.7 +/- 1.07 mmol/l (p<0.001), respectively. Results were compared with those obtained in 23 patients with non-insulin dependent diabetes (15 women and 8 men aged from 48 to 67 years, median age 54.9 +/- 3.34) with disease duration from 6 to 17 years. The above mentioned parameters remained unchanged in these patients. Accumulated data illustrated the hypoglycemic potential of Aronia juice. The precise mechanism of its action is unknown but its beneficial effects and good taste make it a valuable adjunct to the dietary treatment of patients with diabetes mellitus.