OBJECTIVE To determine whether adipose tissue removes a significant proportion of circulating insulin in the obese rat in vivo. METHODS Blood samples were obtained from the carotid artery and the venous side of hind leg muscle, epididymal fat pads and liver (portal and suprahepatic veins), they were used for estimation of insulin disappearance across the tissue. METHODS Anaesthetized Zucker lean (Fa/?) and obese (fa/fa) adult male rats. METHODS Blood flow, glycaemia and insulinaemia. RESULTS In lean rats, the liver accounted for practically all insulin extraction (498 +/- 149 fmol.s-1), removing more than half of the portal insulin in a single pass. In the obese rats, the liver extracted a similar amount in absolute terms (397 +/- 108 fmol.s-1), representing only 16% of portal insulin. In the hind leg muscle of both groups and in the adipose tissue of lean rats, insulin balances were not different from zero; but in obese rats, adipose tissue extracted a similar amount of insulin (405 +/- 127 fmol.s-1) to that removed by the liver. CONCLUSIONS In the Zucker obese rat, peripheral adipose tissue removes as much insulin from the blood as the liver does, in contrast with lean rats, in which the latter is responsible for practically all insulin extraction.