High numbers of yeast, or yeast by products, led to two school-based outbreaks, at the same school, in Cook County, Illinois. In the first outbreak, twenty one persons became ill with vomiting shortly after drinking a mixed, multifruit juice. Laboratory testing of the juice showed high levels of yeast in the product. In the second outbreak, twenty five persons became ill with vomiting shortly after eating a pineapple fruit cup at lunch. Although yeast is not a major food pathogen, their presence in high numbers can cause illness. Poor temperature control can allow yeast to grow in foods