R Using ACAREX test, it is straightforward to determine the a11ergen- containing excreta of housedust mites in dust samples and to detect the sources of a contamination. Investigation of the antigen content by RAST inhibition shows that there is a correlation between guanine and allergen content in a dust sample. There is no direct relation with the number of live (or dead) housedust mites, nor is this to be expected. References 1) Berrens (1975) Naturwissenschaften 62, 29-33. 2) Bronswijk, van, Sinha (1971) J. Allergy 47, 31-52. 3) Bessot, Pauli (1986) Bull. Eur. Phys. Resp. 22, 1-8. 4)...