We have evaluated the levels of red blood cell galactose-1-phosphate uridyltransferase in 20 patients with cataract and in 15 subjects without cataract, suffering from compensated, noninsulin-dependent, type II diabetes. The diabetic patients were compared with a previously examined group of 65 age-matched nondiabetic subjects (25 of whom suffered from bilateral idiopathic cataract). In diabetic patients, the average galactose-1-phosphate uridyltransferase levels tended to be lower and the percentage of cases of reduced enzymatic activity tended to be higher than in the corresponding nondiabetic subjects.