Abstract
Cells derived from the majority of chick embryos, although free of presently known avian tumor virus particles, appear to contain genetic materials similar to those found in this virus group. After infection of these cells with avian leukosis or Rous sarcoma virus, the genetic factor was recovered by incorporation into mature infectious virus. The newly isolated virus (RAV-60) did not require the assistance of another virus for its replication. The virus had most of the attributes of an RNA-containing avian leukosis virus, and its outer structure resembled the Rous sarcoma virus known as RSV(0).