The absolute rate of collagen synthesis by cultured bovine retinal capillary pericytes, determined using the specific radioactivity of proline in the cellular amino acid pool, was compared in media containing different concentrations of glucose (5, 10 or 40 mM) and Sorbinil (0.0 or 0.1 mM), an inhibitor of aldose reductase. The absolute rate of collagen synthesis, in proline molar terms, by pericytes in medium with 5 mM glucose was 3.3 +/- 1.9 (S.D.) pmol 10(-7) cells 24 hr-1, and increased significantly to 8.8 +/- 3.7 pmol 10(-7) cells 24 hr-1 when the glucose concentration was increased to 40 mM. Sorbinil (0.1 mM) reduced the elevated sorbitol contents of pericytes induced by high concentrations of glucose, but did not significantly change the absolute rate of collagen synthesis per cell.