The capsule, cell wall, plasma membrane and nucleus, as well as other intracytoplasmic organelles of Gryptoooccus neoformans were examined by electron microscopy. The capsule, sometimes thicker than cells, consisted of either coiled, intertwining microfibrils or dots; the dot-type appeared with or without radiating cilia-type filaments at the periphery. A clear zone often separated the capsule from the cell wall. The wall appeared to be composed of multiple parallel layers of thin membraneous sheaths containing an inner dense dark zone and an outer lighter area. The plasma membrane was similar to that found in other yeasts. The nucleus showed a clear membrane and generally had disintegrated chromatin material, instead of a definite nucleolus. Mitochondria were consistent in size and shape in most micrographs. Lipid granules with glycogen in transition, large numbers of vacuoles, well preserved ribosomes, few plasmalemmosomes and endoplasmic reticulum were observed. Bud separation demonstrated a simulated break-off appearance from mother cells.The fine structure of yeasts has been the subject of electron microscopical research for many years. Most species investigated have belonged to the genera Candidathe only pathogenic species in this genus remains the least studied for ultrastructure (Edwards, Gordon, Lapa & Ghiorse, 1967;Niki, 1967; Tsukahara, 1963). This study emphasizes the general ultrastructure of the cells of C.neoformans, as well as the capsular sheath. The latter is believed to play an important role in the pathogenecity of this fungus in animals and humans.MATERIALS AND METHODS C. ~0f0rm=ns strain 261C (Littman, DA) obtained originally from a human case, was maintained on Sabouraud's dextrose agar slants at -20°C in the laboratory throughout the last few years with occasional subculturlng to maintain viability. The subcultures were made for 3 generations on the same medium, prior to microscopical study. The yeasts were obtained from 72-hr. slants grown at 37°C, harvested in sterile distilled water and washed 8 times in the same diluent. The final suspension was centrifuged at 3000 rpm. for 10 min. The packed cells were fixed for 3 hr. in glutaraldehyde with Millonig's buffer (pH 7.2), then washed 3 times (5 n~n. each) in the buffer and postfixed for 1 hr. in 2 ~/o osmium tetroxide in the same buffer.The fixed cells were rinsed 3 times (5 rain. each) in Millonig's buffer (pH 7.2), then dehydrated through 25°/o, 50°/o, 70%, 800/0,950/0 and 100% ethanol. The dehydrated ceils were treated with propylene oxide, propylene oxide and Epon 812 (1:1), then *Present address: Dept.