Dermatophagoides farinaeHughes did not survive or reproduce on any of the 45 species of fungi isolated from stored grain, house dust, or human skin scales. Fungi of the generaAspergillus and Penicilliumwere Isolated from the gut of laboratory bredD. pteronyssinusTrouessart. Rearing experiments showed that the culturing ofAspergillus amstelodami(A. glallcusgroup) on mite food medium defatted human dander and yeast greatly enhanced the development and reproduction ofD. pteronysslnus.probably by digesting fatty substances from the human dander and the presence of vitamins in the yeast.It is suggested that in house dust certmn fungi play an Important role In the food chain by predigesting human dander. Members of theA. glaucusgroup could be easily involved because of their high drought resistance and their ability to break down fatty substances in their food medium.