Summary.-Morphological and growth characteristics are described of a rapidly growing cell line with epithelioid and giant-cell characteristics derived from a chondrosarcoma in a male patient 65 years of age. This cell line is of considerable interest because in these cells cross-reacting antigens with known animal oncornaviruses are present. Biochemically, the cells contain particles with a density of 1-16 with " cores " of density 1-23 associated with a reverse-transcriptase-like enzyme and with 70S RNA.