Streptozotocin diabetic rats were divided into two groups. One diabetic group was given an aldose reductase inhibitor (Statil) throughout the study and the other group was left untreated. An additional group of nondiabetic rats was included in the study. After 7 months, the kidneys were perfusion fixed and blocks of tissue were sampled systematically and uniformly throughout the kidney cortex. Plastic embedded blocks were sectioned and used to determine the volume fraction of tubular glycogen by light microscopy. No difference was found between the two diabetic groups in glycogen deposits in the cortical thick ascending limb of Henle's loop, expressed as volume fraction per cortex. Tubules from control animals contained no visible glycogen, as opposed to a content of about 1% in both diabetic groups. We concluded that an aldose reductase inhibitor does not aggravate this tubular lesion (i.e., the Armanni-Ebstein lesion) in rats with experimental diabetes.