gamma-Ray-induced demethylation of thymine in deaerated aqueous solution was observed and quantitatively measured for the first time using thymine-(methyl-14C). An airfree 5 x 10(-5) M aqueous solution was irradiated with doses of 2 x 10(3)-2 x 10(4) Gy. Radio-gaschromatographic analyses provided proof for the formation of methanol (G - 7.6 x 10(-3)), and methane (G = 2.5 x 10(-5)).