Thirty-seven monoclonal antibodies to seven frog virus 3 (FV3) structural proteins were isolated and used to examine the distribution of viral proteins within virions and infected cells. Three monoclonal antibodies, one to the major capsid protein, VP55, and two to VP38 had detectable neutralizing activity suggesting that these proteins are located on the surface of virions. Immunofluorescent studies showed that VP108, VP57, VP55, and VP16 were localized mainly within virus assembly sites, while VP17 was detected in both assembly sites and the surrounding cytoplasm. The abundance of viral structural proteins within assembly sites is consistent with the idea that virion maturation occurs exclusively within assembly sites.