The effect of the development of an experimental granuloma on the urinary excretion of methylated purines was studied in rats applying [ Me- 3H]methionine as a precursor. A distinct increase was observed in the radioactivities 12–16 days after the induction of the granuloma formation, which period coincides with the onset of the synthesis of collagen. The maximal activity was observed in 1- and 7-methylguanines and their specific activities were also increased. The fractionation pattern of the excreted purines was not appreciably altered. The rise in the excretion of radioactive methylated purines is partly due to a change in the methylation of RNA in the liver during the granuloma formation, partly contributed by the nucleic acid metabolism of the granuloma itself.