Various chromogenic chemical tests for Cannabis were evaluated as stains for the microscopical identification of the glandular trichomes of Cannabis sativa. Only vanillin in ethanolic sulphuric acid gave results comparable with the staining obtained with Fast Blue B. The specificity of these two stains was examined using 222 non-Cannabis species from 21 selected plant families. None of the species possessed glandular trichomes which stained with Fast Blue B. Two Mentha and three Callicarpa species had stained glandular trichomes with the vanillin reagent. It is concluded that Fast Blue B is a very specific stain for the cannabinoids in the glandular trichomes of C. sativa L.