The insulin binding characteristics and the structural components of the insulin receptor were studied in the purified liver plasma membranes from seven patients with noninsulin-dependent diabetes (NIDDM) and seven control subjects. In comparison to the controls, diabetic subjects had a 65% reduction in plasma insulin levels in response to an oral glucose load. Specific insulin binding by liver membranes from diabetic patients was, however, twofold greater than the binding activity by membranes from control subjects. This alteration resulted largely from an increase in the number of insulin receptors and a modest increase in receptor binding affinity. Holo (nonreduced) receptor species of similar molecular weights were detected by an affinity labeling technique in the two membrane preparations and sulfhydryl reduction demonstrated an insulin binding subunit of 125,000 mol wt. Overall, these results show that the hepatic insulin resistance of NIDDM cannot be explained by a deficiency in insulin binding.