The fate of 7[14C]-methylguanine after administration to the rat.

1. To assess the significance of the methylation of nucleic acids known to be caused by certain carcinogens, the metabolic fate of 7[(14)C]-methylguanine was studied, with special reference to its possible incorporation into RNA and DNA. 2. The major part (approx. 95%) of the dose was excreted unchanged in the urine. A small amount of N-demethylation took place, as evidenced by the formation of radioactive adenine and guanine, and expiration of (14)C-labelled carbon dioxide. No evidence was obtained for the direct incorporation of 7-methylguanine into systems synthesizing nucleic acids, i.e. RNA in liver, DNA in intestine or in the foetus.