A W/SSM rat strain with symptoms of inherited galactosemia (cataracts, hepatosplenomegaly, aminoaciduria) was previously developed by selection and inbreeding of Wistar rats highly susceptible to the galactosemic effect of galactose. Decreased activity of galactose-I-phosphate uridyl transferase (Gal-I-PUT) in liver and erythrocytes is the salient biochemical feature of the strain. The crossing experiments have shown that the decrease in Gal-I-PUT activity was not required for the expression of main galactosemia symptoms. The experiments excluded low galactokinase activity and high susceptibility of glucose-6-phosphate dehydrogenase and phosphoglucomutase to galactose-I-phosphate as probable reasons of galactosemia. It was shown that increased transport of 14C-galactose to the erythrocytes was characteristic of galactosemic rat strain. The intracellular accumulation of galactose concerned with its increased transport was assumed as a major reason for the development of galactosemia symptoms in W/SSM rats. Genetic analysis has shown that lens lesions in galactosemic rats were controlled by one dominant gene. It is suggested that this gene is responsible for the enhances transport of galactose into the rat cells and its accumulation in toxic concentrations. The main galactosemic symptoms including cataracts result obviously rom the pleiotropic effect of this gene; the decreased activity of Gal-I-PUT may be a consequence of its epistatic effect.