A selective broth for the isolation of Clostridium difficile from stool specimens is described. The broth contains gentamicin, cycloserine and cefoxitin (GCC broth) and gives rapid presumptive evidence of the presence of C. difficile using gas-liquid chromatography. The broth may also be used for the detection of cytotoxin. Final recovery of C. difficile was significantly improved with an increase in isolation rate of 20% in patients in whom fecal cytotoxin could be detected and 125% in patients where fecal cytotoxin could not be detected. Until the pathogenesis of C. difficile-associated diseases is more clearly defined we would stress the importance of isolating the organism, and we advocate the use of a selective broth such as GCC to improve the isolation rate.