Human syncytium-forming (foamy) virus was labeled with 3H-uridine and banded isopycnically in sucrose gradients (buoyant density = 1.16 to 1.18 g/cm3). Viral RNA extracted from the banded virus was analyzed either by rate zonal separation in sucrose gradients or by polyacrylamide-agarose gel electrophoresis. The results indicated that purified HSFV contains a 60S RNA component plus several smaller molecular weight RNA components. On dissociation with heat, smaller RNA structures were released from the 60S component. These results indicate that the genome of HSFV, like the other members of the Retroviridae family, is composed of an aggregate of several RNA species.