A simple method has been devised for testing the pathogenicity of fungal pathogens, especially Hirsutella thompsonii, against the coconut eriophyid mite, Aceria guerreronis. Except one or two bracts of the inner whorl of the perianth, under which an active and healthy population of the mite was thriving, the rest of the five or four bracts were removed from a young nut and a suspension of conidia was injected into the thin space between the nut surface and the inner surface of the bract/s by gently lifting the bract/s but leaving it/them intact. The meristematic region of the nut that got exposed after the removal of bracts as well as the retained bract/s were sheathed with a stretched parafilm up to the green portion of the nut in such a manner that there were no gaps. The treated nuts were incubated under ambient conditions. At the end of 96 h, the parafilm was unwound and the bract/s was/were opened to observe infected mites on the inner surface of the bract/s and/or on the nut surface just below the detached bract/s under a stereozoom microscope. The fungus was isolated from the infected mites and upon fresh inoculation it could again produce disease in the mites and exhibit the same microand macro-morphology in culture after the second passage as well, thus satisfying Koch's postulates.