SUMMARY 1. A method of using guinea-pigs and mice to detect pathogenicity in strains of C. albicans is described. 2. Agglutination of C. albicans by the slide method has been shown to be reliable. 3. Seventy-eight strains of yeast-like organisms have been submitted to a number of tests to decide upon a method of identifying C. albicans. The tests were fermentation reactions, formation of hyphae and chlamydospores in corn-meal extract, animal pathogenicity tests, slide agglutination with an absorbed anti-serum and colony appearance on eosin-methylene blue agar. No single test was completely accurate. 4. Eosin-methylene blue agar is a valuable medium for isolating and detecting C. albicans. 5. Slide agglutination gives the smallest number of errors where a reasonably rapid decision has to be made.