The selective degeneration of retinal mural cells, a hallmark of early human diabetic retinopathy, has also been reported to occur in both diabetic and galactose-fed dogs. By employing antibodies raised against purified dog lens aldose reductase the presence of aldose reductase can be immunohisto-chemically demonstrated in the cytoplasm of mural cells but not endothelial cells of dog retinal vessels isolated by trypsin digestion. This immunohisto-chemical staining is similar to that observed with isolated human retinal vessels.