The activity of red blood cell galactose-1-P-uridyl transferase in 22 patients with congenital and infantile cataract and in 18 age-matched controls was investigated. All control subjects examined showed normal enzymatic levels, while 31.8% of patients with congenital and infantile cataract presented a statistically significant reduced enzymatic activity (mean--2 SD in controls). Twenty-four parents of children with congenital and infantile cataract were also examined. Four parents were affected by congenital cataract and the other 20 showed transparent lenses. The parents were compared with a group of 20 age-matched control subjects examined previously. There was no difference in the average enzymatic activities between the groups. The results suggest that a chronic disorder of galactose metabolism may be involved in the development of congenital and infantile cataract.