Five African green monkeys inoculated intratracheally with 7.5 x 10 (3) to 1.4 x 10 (5) plaque-forming units of simian varicella virus (SVV) were subjected to clinical, laboratory, pathologic, and virologic analyses to study the pathogenesis of acute varicella. All animals developed viremia and rash and were sacrificed 8 to 11 days post-infection. No serum was available for postmortem serologic studies. Examination of multiple organs for pathologic changes and for SVV-specific antigen and nucleic acid revealed inflammation, hemorrhagic necrosis, and intranuclear Cowdry A inclusions in liver, lung, lymph node, and spleen; mild inflammation without necrosis in adrenal gland, kidney, and bone marrow, and SVV-specific antigen and nucleic acids in all viscera examined. No pathologic changes, SVV antigen or nucleic acids were detected in the spinal cord or in the brain from any of the monkeys. Ganglia revealed mild inflammation but no necrosis, and intranuclear inclusion bodies in non-neuronal cells of one trigeminal ganglion; SVV antigen and nucleic acids were detected in both non-neuronal and neuronal cells in ganglia. The pathologic and virologic findings in viscera are consistent with those described in viscera of humans with disseminated zoster, but the mild inflammatory changes in ganglia during acute simian varicella infection contrast with the extensive hemorrhagic necrosis and intranuclear inclusion bodies seen in human ganglia after disseminated varicella or zoster. Nevertheless, these studies show that ganglia become infected with varicella virus during primary infection, although the route of primary ganglionic infection remains to be determined, and indicate the possible usefulness of the SVV model to study varicella pathogenesis in humans.