Since airborne basidiospores may be important inducers of respiratory allergy, extracts of spores, caps and mycelia from Pleurotus ostreatus were studied by immunologic techniques. Crossed immunoelectrophoresis of the Pleurotus spore extract showed it to be a complex mixture containing at least 27 precipitating antigens. Crossed-line immunoelectrophoresis comparing Pleurotus spore extract with extracts of Pleurotus cap or mycelia demonstrated both common antigens and antigens unique to the spore extract. Inhibition of Pleurotus spore RAST by extracts of Pleurotus spore, cap, and mycelia suggested that these extracts contained common allergenic components. However, wheal and flare skin reactivity of allergic patients to extracts of P. ostreatus or Cantharellus cibarius demonstrated little correlation between reactivity to cap and spores. These results demonstrate that basidiomycete spore extracts are the best diagnostic reagents to use in clinical studies, although cap and mycelia extracts may provide useful material for further allergen analysis.