A technique for catheterization of a vein draining abdominal subcutaneous tissue and a microdialysis technique that allows measurements of intercellular water concentrations in adipose tissue in humans have recently been described. In the present study, we compare the two techniques during an oral glucose load. In addition a technique using microdialysis for measurement of tissue oxygen and carbon dioxide tensions is described. Microdialysis and vein catheterization were performed in the same region on the abdomen, and the subcutaneous adipose tissue blood flow was measured by the local 133Xe washout method. The results show that subcutaneous adipose tissue gas tensions are on level with gas tensions measured in abdominal venous blood. Comparison of metabolite concentrations measured in the venous blood and venous blood concentrations calculated from microdialysis data shows that there is good agreement between the concentrations obtained by the two techniques with respect to glucose and glycerol, whereas lactate concentrations are very different. With regard to substrate fluxes calculated by Fick's principle, the catheterization technique is probably the most reliable, considering the numerous assumptions on which calculations of venous concentrations from microdialysis data are based. Advantages and disadvantages of the two techniques are discussed.