The pattern of distribution of galactose and its metabolites was determined in tissues of mice deficient in galactose-1-phosphate uridyl transferase (G/G) 4 h after the administration of 1mg/g of [13C]galactose. Labeled galactose was found in all the tissues examined, the highest amounts in liver and kidney. Each of the tissues had its own pattern of labeling of galactose-1-phosphate (gal-1-P), galactitol and galactonate. [13C]gal-1-P and galactonate concentration was highest in liver while [13C]galactitol was higher in kidney and heart than in other tissues. Muscle had the lowest amounts of these compounds. In contrast, no galactose was found in tissues of normal mice (N/N) except for a minute amount in muscle. No [13C]gal-1-P was found in liver, kidney or brain and only minute amounts in heart and muscle of N/N animals. Barely detectible, labeled galactitol was observed in these tissues except liver, where none was found. [13C]Galactonate was formed in liver comparable to G/G mice. Almost all of the accumulating 13C isotope was found in liver and kidney glucose and lactate in the normal animals. [13C]Glucose and lactate was also found in liver of the G/G animals, but to a lesser extent than in normals, indicating the presence of a pathway in G/G animals for circumventing the block at GALT for the normal conversion of galactose to glucose.