Organic dust toxic syndrome (ODTS) is associated with inhalation of high concentrations of organic materials and is a noninfectious illness characterized by fever, malaise, myalgia, and neutrophilic inflammation of the lower respiratory tract. Studies in our laboratory of fungi in fresh lumber have demonstrated that yeasts may predominate and have raised the issue of potential exposure of sawmill workers to yeasts. Zymosan, a cell wall preparation from Saccharomyces cerevisiae, is a potent stimulator of alveolar macrophages (AM). In the present study, preparations from the cell walls of Pichia fabianii, Candida sake, Trichosporon capitatum, Rhodotorula glutinis, and Cryptococcus laurentii were compared with zymosan and β-1,3-glucan for their ability to stimulate AM and activate complement. All species activated complement. P. fabianii, C. sake, T. capitatum, R. glutinis, C. laurentii, as well as zymosan and glucan, stimulated superoxide anion and leukotriene B4 production in a dose-dependent fashion, but R. glutinis and C. laurentii were much less active. Zymosan, glucan, P. fabianii, and R. glutinis treatment of AM resulted in increased phagocytosis of labeled sheep RBCs, whereas there was no effect with C. sake or C. laurentii and T. capitatum significantly inhibiting phagocytosis. These results suggest that exposure to high concentrations of yeast could provoke pulmonary inflammation resulting in an episode of ODTS.