Diabetes is known to be associated with an increase in aldose reductase activity, platelet hyperaggregability, lipid peroxidation, and cataract formation. A molecule, D-myo-inositol 1,2,6-trisphosphate (PP-56), derived from phytic acid, could in principle, by supplying myoinositol to tissues and acting as an antioxidant, counteract some of the manifestations of diabetes. Thus, the effects of PP-56 on platelet aggregation, fatty acids, and polyols were investigated in uncontrolled streptozotocin-induced diabetes in rat in relation to cataract and lipid peroxidation. A decrease in the response of platelet aggregation to thrombin and ADP (P less than 0.05, P less than 0.001) and in the level of sorbitol and the ratio sorbitol/myo-inositol (P less than 0.01) in platelets was observed in the rats treated by PP-56 for 7-8 weeks. These beneficial effects were associated with an incidence of cataract reduced by 26 to 44% (P less than 0.05 to P less than 0.001) depending on the duration of treatment. They were also accompanied by a significant lower plasma level of malondialdehyde (P less than 0.05), and, more markedly, of conjugated dienes (P less than 0.001) as well as an increase in platelet lipids of the 20:4(n-6)/20:3(n-6) ratio, an index of delta 5 desaturase activity. PP-56 appears to modulate fatty acid desaturases and aldose reductase in platelets and delay by a few weeks the development of cataract in this acute model of diabetes.