A 68-year-old man with intermittent fever of unknown origin was found to have a systemic Saccharomyces infection, probably as a result of daily oral ingestion of the organism as brewer's yeast, a nutritional supplement. The case illustrates the potential dangers that may occur secondary to the oral ingestion of viable microorganisms, and the disease-producing potential of Saccharomyces is reaffirmed. Once again, a thorough and complete medical history was the key to resolving an unusual fever of unknown origin.