A virus was found in the ovarial calyx tissue of Mesoleius tenthredinis, an ichneumonid parasitoid; the "infection" was present in all females thus far examined. Virions were morphologically similar to typical baculoviruses. Apparent uncoating of viral nucleocapsids at nuclear pores was observed, indicating the reinfection of the calyx epithelium may occur. Electron microscopy of DNA extracted from calyx tissue suggests that the viral genome may be circular, and of high molecular weight.