Kalckar et al.1,2have recently succeeded in demonstrating the locus of the metabolic block which occurs in the red cell and liver of individuals suffering from congenital galactosemia. A similar block has been demonstrated in the lenses obtained from a child who died of this disease.3In all these tissues there is a relative or absolute lack of the enzyme galactose-1-phosphate uridyl transferase with the subsequent accumulation of galactose-1-phosphate (Gal-l-P) in the red cell, liver,1,2and in the lens.4This ester apparently accumulates to about ten times the level normally present in these tissues.1,2,4Since the metabolism of glucose provides the lens with its main source of energy, it seems likely that an accumulation of Gal-1-P within the lens may be the precipitating factor in the development of both the human and the experimental galactose cataract. There are several possible loci where this ester could