SUMMARYThe genome of a rod-shaped virus, aa, isolated from Spiroplasma citri, has been examined. Electron microscopy and single strand-specific $l nuclease digestion showed that the genome is a single-stranded circular molecule of 8.5 kilobases. Two replicative forms of DNA have been isolated, a supercoiled double-stranded circular molecule and a nicked form derived from it. A physical map of the replicative forms has been constructed.