Extracts from two standard dusts were equally capable of stimulating prostaglandin production by rabbit alveolar macrophages. Activity was associated with both the non-polar organic solvent fraction and the residual aqueous fraction. Two distinct types of compounds appear to be responsible for this stimulation. Extracts from these same dusts and bracts also caused immediate strong contractions in isolated cockroach hindgut muscle. Repeated exposure did not desensitize the hindgut muscle. Two types of activity were observed; that from the ether solubles of aqueous extracts was much more potent than that from 70% acetone extracts. The activity was consistently obtained from the aqueous acetone; the ether fraction frequently had no activity. Preliminary data suggests that the active agent in the aqueous acetone is a tannin.