Elevated fasting plasma non-esterified fatty acid (NEFA) levels have been reported in Type 2 diabetes. We examined whether such changes persist during low-grade exercise and influence carbohydrate metabolism. Eight Type 2 diabetic patients with moderate glycaemic control and eight healthy controls received the anti-lipolytic agent, acipimox, or placebo on separate occasions before exercising for 45 min at 35% pre-determined VO2max. Fasting plasma NEFA levels were similar (0.40 +/- 0.06 (SEM) and 0.45 +/- 0.05 mmol l-1; healthy and Type 2 diabetic subjects) following placebo, and increased to comparable levels with exercise (0.73 +/- 0.07 and 0.73 +/- 0.10 mmol l-1). Acipimox lowered basal NEFA levels (0.14 +/- 0.03 and 0.28 +/- 0.04 mmol l-1; both p < 0.05 vs placebo), and prevented the rise with exercise. Blood glucose (p < 0.001) and serum insulin (p < 0.01) levels were higher in the Type 2 diabetic patients (vs controls) for both treatments. Whole body lipid oxidation increased from baseline to a comparable degree with exercise following placebo (3.2 +/- 0.3 and 2.8 +/- 0.3 mg kg-1 min-1; healthy and Type 2 diabetic subjects, both p < 0.02). Although less marked, the same was also observed following acipimox (2.0 +/- 0.4 and 2.1 +/- 0.5 mg kg-1 min-1; both p < 0.05). Carbohydrate oxidation increased with exercise in both subject groups, but with no significant difference between the treatments. Thus, the metabolic response to low-grade exercise was normal in Type 2 diabetic patients with moderate glycaemic control, but occurred against a background of hyperinsulinaemia.(ABSTRACT TRUNCATED AT 250 WORDS)