Reducing the rate of glucose absorption is a useful approach to the treatment of noninsulin-dependent diabetes mellitus (NIDDM). Intestinal absorption of glucose and amino acids is known to be increased in diabetes in laboratory animals but has not been systematically studied in human NIDDM subjects. In this study the intestinal absorption of glucose and glycine was measured during steady-state perfusion of the jejunum in 10 NIDDM subjects and in 11 healthy volunteers. Absorption rates were linearly related to solute load for both glucose and glycine. Over the range of solute concentrations, absorption rates of glucose (F = 4.38, p less than 0.05) and glycine (F = 7.07, p less than 0.02) were slightly reduced in diabetic subjects. The reduction in absorption rates may be accounted for by differences in age and diet between the groups. It is concluded that glucose and amino acid absorption is not increased in human NIDDM.