In this study, activity of some of the key enzymes participating in purine metabolism was measured in cancerous and noncancerous human kidney tissues from 18 patients with renal cell carcinoma. Twelve cancerous tissues were at stage T-1-T-2 and 6 tissues were at stage T-3-T-4. Adenosine deaminase (ADA) and guanase (GUA) activity was increased and xanthine oxidase (XO) activity decreased in cancerous tissues compared to noncancerous ones. No difference was, however, found between 5'-Nucleotidase (5'-NT) activity of the tissues. There were also no statistically meaningful differences between the enzyme activities of the cancerous tissues at stage T1-2 and T3-4. Results suggest that the changes observed in the activity of the enzymes participating in purine metabolism result from accelerated DNA turnover in the cancerous tissues and cells, and these changes might provide selective advantage, possibly by causing acceleration of salvage pathway activity, to the cancer cells to grow and develop more rapidly.