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) Tovey,Chapman,Wells,Platts-Mills (1981) Am. Rev. Resp. Dis. ~,630-635. 5) Bischoff (1986) A11ergo1. Fortbi1dung Bd. 1, in press. 6) Tovey, Chapman, Platts-Mills (1981) Nature 289, 592-593. 7) Tovey, Chapman, Platts-Mills (1980) Clin. ATTergy 10, 466-467. 8) Chapman, Heymann, Sutherland, Platts-Mills (1985) Tnt. Archs Allergy appl. Immun. 77, 166-168. 9) Bischoff (1986T Swiss Med 8, 39-44. 10) Bischoff, Bronswijk, van (1986) Allergologie 9, 375-378. 11) Bronswijk, van (1973) J. Med. Ent. 10, 63-70.- 12) Bischoff,Schirmacher(1984)Allergol.~446-449,and (1985)Allergol.8,36-38. 13) Bischoff, Schirmacher, Schober (1985) Allergol. 8, 97-99. - 14) Bischoff, Fischer, Wetter (1986) Allergol. 9, 171-176. 15) Bischoff, Liebenberg, Wetter (1986) AllergoT. 9, 287-292. 16) Bischoff, Krause-Michel, Nolte (1986) Allergol~ 9, in press. 17) Mitchell, Wilkins, r~cCallum Deighton, Platts-~lilTs (1985) Clin. Allergy 15, 235-240. 18) Bronswi jk, Bi schoff, Schi rmacher, Berrens, Schober (1986) J. ~led. Entomo1. 23, 217-218. 19) Bronswijk~van, Exp. and appl. Acarology, in press.