Saccharomyces boulardii (Sb) is a particular strain of Saccharomyces cerevisiae (Sc). This viable yeast is used in intensive care adult patients, delivered in packets of 500 mg, for preventing diarrhea associated with antibiotics or enteral feeding at a regimen of 1-2 g/day. Between June 1996 and October 1998, seven cases of fungemia with Sb occurred in a 12-bed intensive care unit (ICU). All the patients concerned were severely ill patients, mechanically ventilated, treated by broad spectrum antibiotics with central venous catheter and were pretreated with Sb, except for one patient. In this study, Sb was identified by specific mycologic methods and confirmed the genomic identity between isolates of blood culture and yeasts from the treatment packets, contrary to a few other reports concerning Saccharomyces species published in international literature. The hypothesis discussed for explaining these cases of Sb fungemia are: (1) an intestinal translocation of Sb administered at a high dosage in severely ill patients, (2) a contamination of the central venous catheter, especially in the patient not pretreated with Sb and (3) a massive colonization of critically ill patients by the yeast as has been reported for Candida species. We note that cases of fungemia with Sc and Sb have become more and more frequent in the international literature during the last 10 years and we do not recommend administering Sb treatment in critically ill patients.