The effects of allopurinol and 4-aminopyrazolo [3, 4-d] pyrimidine (4APP) on adenine-induced renal injury in mice were examined. Plasma urea nitrogen (UN) and creatinine levels increased after the oral administration of adenine to mice. However, plasma UN and creatinine levels decreased inversely with the dose of 4APP when a different dosage of 4APP was administered together with adenine. Yet 4APP did not have any effect on the UN or creatinine levels when 4APP was administered after adenine administration. Plasma UN and creatinine levels increased in the allopurinol-administered group as in the adenine-administered group. Moreover, from light microscopic observation by hematoxylin-eosin staining, microvacuolic changes in the proximal tubuli were detected in the mouse kidney in the adenine-administered group, and epithelial cell loss, degeneration and microvacuolic changes in the proximal tubuli were observed in the mouse kidney in the adenine-and-allopurinol-administered group. However, there were no changes in the proximal tubuli in the mouse kidney in the adenine-and-4APP-administered group. These findings suggested that 4APP inhibits the action of adenine in the mouse kidney.