Prereduced, anaerobically sterilized peptone yeast glucose broth was supplemented with p-hydroxyphenylacetic acid and used for the presumptive identification of Clostridium difficile. Two hundred eighty-two organisms were grown in this medium for 18 h and tested for p-cresol production by gas-liquid chromatography. All 49 stock and reference strains of C. difficile and 19 organisms confirmed as C. difficile produced p-cresol. p-Cresol was not produced by 53 negative control or 161 test organisms. The system was convenient and effective.