Microdialysis of the abdominal subcutaneous tissue was performed in seven healthy normal weight subjects after an overnight fast and also after oral ingestion of 100g glucose. The lactate concentration in the interstitial water was compared with that in the venous and arterialized plasma from the cubital veins. In the postabsorptive state the lactate concentration in the subcutaneous tissue (1128 +/- 72 mumol/l, mean +/- SEM) was significantly higher (p less than 0.01) than that in both arterialized (722 +/- 72 mumol/l) and venous plasma (798 +/- 41 mumol/l). The oral glucose load further increased the lactate level in the subcutaneous tissue throughout the observation period of 2h. The kinetics for the increase in the lactate concentration was not apparently different in blood or tissue. The highest lactate levels were 1798 +/- 173 mumol/l in the subcutaneous tissue and 1199 +/- 150 mumol/l and 1275 +/- 123 mumol/l in arterialized and venous plasma, respectively. It is concluded that abdominal adipose tissue produces lactate both in the fasting state and after an oral glucose load. The data emphasize the importance of the adipose tissue as a significant source of lactate production in the body.