Liver biopsy specimens of two patients with Reye syndrome were examined for ultrastructural features, viral isolation, and urea-cycle enzyme activity. Concurrent presence of herpes-like virus and myxovirus/paramyxovirus was demonstrated by electron microscopy, and viral infections were confirmed by isolation or serologic tests. A concomitant hepatic ornithine transcarbamoylase deficiency was also noted. The pathogenesis in these instances seems to consist of an initial synergistic insult on the liver by mixed types of viruses and subsequent breakdown of urea cycle, Krebs cycle, and possible other hepatic functions. An exodus of glycogen granules into the hepatic spaces of Disse and sinusoids suggests that the viruses have injured the plasma membranes as well as the mitochondria of hepatocytes. Since Kapila et al reported similar disorders five years before Reye et al, the name of Kapila-Reye disease is suggested.