The effect of 6-mercaptopurine and allopurinol on granulopoiesis.

The effect on granulopoiesis of 6-mercaptopurine alone, and in combination with allopurinol, was studied in mice using an in vitro colony-forming assay for granulocytic progenitor cells. The combination of 6-mercaptopurine and allopurinol pro duced significantly greater suppression of de novo granulo poiesis than did 6-mercaptopurine alone. Allopurinol in very high doses was found to be myelosuppressive. The possible implications of these findings are discussed.