SUMMARYThe growth of the wood-rotting fungi,Polyporus tulipiferus, P. palustris, Lenzites trabea, Fomes subroseus, Peniophora giganteaandLentinus lepideus, was determined in L-, D- and DL-alanine and in L-, D- and DL-aspartic acid, separately, in shake culture in a basal synthetic medium. Generally, the amounts of growth in the racemic mixtures at 0.003 per centtotalnitrogen concentration approximated one-half of that in the L-isomers at the same total nitrogen concentration, as would be expected if the D- forms were not utilized and the amounts of growth were directly proportional to the“utilizable”(L-) nitrogen concentrations. Generally, also, mycelial weights in the racemic mixtures at 0.006 per cent total nitrogen were the same as the amounts of growth in the respective L-isomers at 0.003 per cent nitrogen, and approximated double the growth in the racemates at 0.003 per cent nitrogen. In no case was there utilization of D-isomers alone, and in only one case ---L. trabeain alanine---was there some evidence for the assimilation of the D-isomer of the racemate in the presence of the L- form. In one or two cases there was a suggestion of some inhibition of growth by the D- form in the racemic mixture. The isomeric configuration of amino acids is an important factor in their utilization by wood-rotting fungi.