The reaction between L-ascorbic acid and L-tryptophan in phosphate buffer (pH 7.0) at 37° for 2 months gave several reaction products of which 2 were mutagenic on S. typhimurium TA 100 in the absence of S-9 Mix. The structure of these 2 compounds were determined to be 1-(2-furyl)-pyrido [3, 4-b] indole and 1-(2-furyl) pyrido [3, 4-b] indole-3-carboxylic acid respectively by their mass spectral and 13C NMR analysis.