L-[2,4,5,6,7-2H5]Tryptophan was incorporated into roquefortine 2 by Penicillium roqueforti and aszonalenin 3 by Aspergillus zonatus with retention in each case of five deuterium atoms; that 5a-hydrogen of both metabolites is derived from the 2-hydrogen of tryptophan. © 1993.