Infected tissues from four patients with disseminated candidiasis were examined by electron microscopy in order to study the host-parasite relationship at the cellular level. Blastospores and pseudohyphae were capable of invading parenchymal cells in the spleen, liver, myocardium, kidney, and esophageal and rectal mucosa. The Candida cells were typically well preserved despite the autolytic changes in parenchymal cells. Extracellular fungi were often coated with fibrin or associated with capillary thrombi, which suggests that Candida cells synthesize a procoagulant substance. The outer flocular coat of the yeast cell appeared to be partially of host origin since it diminished in thickness when organisms were cultured in media devoid of serum protein. Organisms cultured in vitro were ultrastructurally similar to those that invaded tissue.