Without the isolation of the causitive organism, the diagnosis of cryptococcosis currently relies heavily on clinical findings and the careful exclusion of such confusing entities as tuberculous meningitis. Dependable serologic confirmation of the diagnosis is greatly needed in view of the prognosis of the disease and the availability of Amphotericin B treatment. Since the patient seldom comes to the attention of the physician until at least several weeks or months have elapsed, one may expect that an immunologic response has had ample time to develop. For demonstrating antibodies, the indirect fluorescent straining technique as reported here affords a most sensitive approach. 1 Materials and Methods In the test, heat-killed Cryptococcus neoformans cells are fixed on a microscopic slide and covered with heat-inactivated serum from the patient. After suitable incubation and washing with saline-buffer, a Coombs reagent (antihuman globulin) tagged with fluorescein-isothiocyanate is applied. If antibody from the patient's serum is