Under conditions of dietary galactose loading, mice deficient in galactose-1-phosphate uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90+/-1.62 (M+/-SE) and 38.88+/-2.62 micromol/g tissue, respectively, levels 40-100 times that of galactose-1-phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO2, since the compound is an intermediate in an alternate route for galactose disposition.