A particular strain of Saccharomyces cerevisiae, Hansen CBS 5926 (syn. S. boulardii), is commonly used as biotherapeutic agent for the prevention and treatment of antibiotic associated diarrhea. Recently, cases of fungemia with S. cerevisiae have increased especially in immunosuppressed or critically ill patients treated with S. boulardii. And S. boulardii administered can simply pass into stool and be isolated as S. cerevisiae. In cases of S. cerevisiae isolated from clinical specimens, it should be required to confirm the relatedness with administration of biotherapeutic agent composed of S. boulardii. A 61-year-old woman who had persistent urinary tract infection by C. tropicalis, developed absolute neutopenia, fever and watery diarrhea and treated with Bioflor composed of S. boulardii, amikacin, ceftriaxone, metronidazole and fluconazole during 3rd chemotherapy against bladder cancer with liver metastasis. On KOH smear of stool specimen, yeasts were observed and the yeasts were identified as S. cerevisiae. She was diagnosed as fungal enterocolitis and sepsis and treated with amphotericin B, but considering her clinical course, S. cerevisiae was presumed not to be a pathogen, but to be a simple passage of S. boulardii administered from intestine. We report a case of S. cerevisiae isolated from stool specimen of a patient administered Bioflor with literatures review. (Korean J Clin Microbiol 2003;6(2):168-171)