Bronchoprovocation challenge with basidiospore extracts was performed in eight subjects with asthma and with positive wheal-and-flare skin reactivity and RAST to basidiospore allergens. Five of the eight patients demonstrated a significant decrease in FEV1 ranging from 20% to 47% after basidiospore-extract challenge. Both immediate and late-phase reactivity was observed. Six atopic control subjects with asthma and with negative skin reactivity to basidiospore extracts did not exhibit significant bronchospasm after basidiospore challenge. These results demonstrate that basidiospore extracts can induce bronchospasm in subjects with asthma who demonstrate IgE antibodies to basidiospore allergens.