The sensitizing capacity of brewer's yeast (Saccharomyces cerevisiae) was studied with the skin prick test method in 449 subjects, including 226 atopic dermatitis (AD) patients, 50 patients with allergic rhinitis (AR) and/or asthma (A), and 173 nonatopic controls. A positive SPT reaction (> or = + +) was seen in 94% of patients with severe AD, in 76% with moderate AD, and in 25% with mild AD or no history of AD. Patients with AR and/or A and nonatopic controls displayed a positive reaction in only 8 and 2% of cases, respectively. There was also a parallel skin prick test reactivity with other yeasts including Pityrosporum ovale and Candida albicans, suggesting cross-reactivity. Parallel skin reactivity was observed also with molds and animal dander but not with pollen or house-dust mite. A significant correlation was also found between total serum IgE level and skin prick test (SPT) results with S. cerevisiae.