A wide range in growth responses was obtained by two isolates each of Sclerotinia trifoliorum Erikss. and S. sclerotiorum (Lib.) d By. in stationary culture in a synthetic liquid medium containing a number of nitrogen sources representing both organic and inorganic forms. Good sources of nitrogen were casein hydrolysate, L-proline, DL-asparagine, L-arginine, L-glutamic acid, L-aspartic acid, L-histidine, L-alanine, ammonium chloride, ammonium nitrate, L-tryptophan, ammonium sulfate, and DL-phenylalanine. Poor nitrogen sources included potassium nitrite, sodium nitrite, DL-lysine, L-valine, L-cysteine, DL-threonine, and DL-methionine. An additional eight sources were intermediate in the amount of growth supported. Growth by the S. trifoliorum isolates on the ammonium nitrogen sources was significantly greater than on the nitrate sources. No such difference was observed for the S. sclerotiorum isolates. DL-Phenylalanine ranked much lower and L-glutamic acid and calcium nitrate much higher as nitrogen sources for the S. sclerotiorum isolates than for S. trifoliorum isolates. Significant differences between the isolates of each species were observed on a number of nitrogen sources.