Green and black teas were given at 1.25% in the drinking water to streptozotocin-induced diabetic rats for 3 months. Normal and diabetic control groups were also studied. As expected, diabetic animals had significantly increased glucose in lens and plasma. Lens and red blood cell sorbitol were significantly increased as a result of the aldose reductase pathway activation. Plasma and lens lipid thiobarbituric acid-reactive substances and protein glycation were also significantly elevated. Both teas significantly inhibited diabetic cataracts and caused significant reductions in the biochemical pathway implicated in the development of the pathology. After corrections for glucose, it was found that the teas retard the development of diabetic cataracts by a hypoglycemic effect that in turn inhibits the biochemical indicators of pathology. There were significant correlations between glucose, cataract score, and these indicators. Green tea but not black tea caused a significant decline in triglycerides in the diabetic animals. Tea may be a simple, inexpensive means of preventing or retarding human diabetes and the ensuing complications. Tea also should be investigated as an adjunct therapy for diabetes treatment.