We measured erythrocyte aldose reductase and sorbitol dehydrogenase activity in erythrocytes in healthy individuals aged from 16 to 91 years to determine the mechanism of age-dependent sorbitol accumulation. Erythrocyte aldose reductase activity increased significantly with age but ageing had no effect on sorbitol dehydrogenase activity. Age and the aldose reductase/sorbitol dehydrogenase ratio were positively correlated. These findings suggest that an increase in the ratio of aldose reductase to sorbitol dehydrogenase may contribute to the tissue accumulation of sorbitol in the elderly and may be a mechanism of a disease that is common in elderly individuals.