To measure interstitial glycerol and lactate production from the sc adipose tissue of two regions in nine black and nine white lean men, sc microdialysis was performed in combination with adipose tissue blood flow rates measured with 133Xe clearance. In the postabsorptive state, the plasma glucose and insulin levels of the black men and white men were similar. The black men had higher plasma free fatty acids (825+/-97 vs. 439+/-58 micromol/L; P < 0.005), glycerol (99.5+/-5.1 vs. 54.1+/-3.3 micromol/L; P < 0.0001), and lactate (1056+/-95 vs. 729+/-45 micromol/L; P < 0.01). Interstitial glycerol concentrations in the black and white men were 227 vs. 163 micromol/L (P < 0.01) and 230 vs. 162 micromol/L (P < 0.05) in the abdominal and femoral regions. The adipose tissue blood flow rate was higher in the black men in the abdominal (7.9+/-0.9 vs. 3.1+/-0.5 mL/100 g x min; P < 0.01) and femoral area (5.2+/-0.6 vs. 2.8+/-0.3; P < 0.01). Interstitial lactate concentrations in black and white men were 1976 vs. 1364 micromol/L (P < 0.004) and 1953 vs. 1321 micromol/L (P < 0.004) in the abdominal and femoral regions, respectively. Glycerol release was higher in black men vs. white men for abdominal (0.21+/-0.02 vs. 0.14+/-0.02 micromol/100 g x min; P < 0.02) and femoral (0.22+/-0.02 vs. 0.15+/-0.01; P < 0.05) areas. Postprandially, black men had higher plasma glucose levels [1 h, 9.6+/-0.4 vs. 8.2+/-0.5 mmol/L (P < 0.05); 2 h, 8.9+/-0.4 vs. 7.2+/-0.4 mmol/L (P < 0.01)], but lower plasma insulin levels [1 h, 173+/-13 vs. 264+/-48 pmol/L (P < 0.05); 2 h, 136+/-20 vs. 209+/-34 pmol/L (P < 0.05)]. Plasma free fatty acid, lactate, and glycerol levels remained higher in the black men. After 1 h, lactate release was higher in the black men vs. that in the white men for abdominal (20.5+/-1.6 vs. 14.7+/-2.5 micromol/100 g x min;P < 0.05) and femoral (15.6+/-1.1 vs. 12.1+/-1.8; P < 0.03) areas. We conclude that the black men, who are relatively insulinopenic postprandially, have a brisker lipolysis and also release more lactate from sc fat tissue than white men. These differences in adipose tissue metabolism may be related to differences in the lipid profiles and glucose metabolism previously documented in these ethnic groups.