Three captive banded rock rattlesnakes (Crotalus lepidus klauberi) died at Taronga Zoo, Sydney, Australia, between 1984 and 1987 with similar lesions in each case. Grossly, the liver and kidneys had multiple grey, fleshy nodules replacing much of the parenchyma. Histologically, these lesions were massive accumulations of yeast-like organisms, located mainly within macrophages in capillaries and sinusoids. There was little other inflammatory reaction. Organisms also were seen in the muscle and adventitial coats of the intestine, in the spleen, pancreas, brain, lungs, ovary, and fat body. Apparent budding was observed in fresh smears, and the organisms stained Gram-positive and periodic acid-Schiff positive but failed to grow on routine fungal media. Based on transmission electron microscopy, the organisms were typical yeast cells with thick, apparently single-layered cell walls showing evidence of enteroblastic proliferation. Two of the snakes had concurrent bacterial infections.