Non-insulin-dependent diabetes mellitus (NIDDM) is associated with an increased cardiovascular risk. Glycaemic control alone is often insufficient to control diabetic dyslipidaemia and other cardiovascular risk factors associated with NIDDM. The present trial was designed to evaluate the effects of physical activity as an adjunct to standard diabetes therapy on the lipid profile, blood pressure, glycaemic control, weight and body fat. Sixteen well-controlled (HbA1c 7.5%) patients with NIDDM participated in a regular aerobic exercise training programme at 50-70% maximal effort over 3 months. Thirteen age- and sex-matched patients with NIDDM served as a control group. The 3-month intervention with an increase in physical activity from 92 (mean +/- SD) +/- 79 to 246 +/- 112 min per week (p < 0.001) by means of a structured activity programme resulted in significant improvement of plasma lipids with a 20% decrease in triglycerides (p < 0.05), unchanged total cholesterol and increases in high-density lipoprotein and high-density lipoprotein-3 subfraction of 23% (p < 0.001) and 26% (p < 0.001), respectively. Systolic and diastolic blood pressure decreased significantly from 138 +/- 16 to 130 +/- 17 mm Hg (p < 0.05) and 88 +/- 10 to 80 +/- 10 mmHg (p < 0.001), respectively. Resting heart rate decreased from 81 +/- 13 to 74 +/- 14 beats per minute (p < 0.001), waist-hip circumference ratio decreased from 0.96 +/- 0.11 to 0.92 +/- 0.10 (p < 0.001) and body fat decreased from 35.3 +/- 7.2 to 33.0 +/- 8.0% (p < 0.001). These effects occurred independently of changes in body weight and glycaemic control, which did not change during the study. This study shows that improvement in physical fitness by introducing regular physical exercise as part of the treatment programme in patients with NIDDM results in a significant amelioration of their cardiovascular risk profile.