Canine transmissible venereal sarcoma (CTVS) is a contagious neoplasm which regresses spontaneously in adult dogs but metastasizes and kills puppies transplanted with the neoplasm at a very young age. Immunofluorescence studies showed that 30 +/- 14% of cells from steady-state and 22 +/- 7% of cells from regressing tumors had membrane-bound antibodies which could be eluted out with warm washes at 24 degrees C, whereas the cells from progressor tumors had very little such antibody (6 +/- 6%). Time-course kinetics of anti-CTVS antibodies in the serum of tumor-bearing dogs did not correlate well with tumor volume, however, the presence of such antibodies in adult dogs (47 +/- 13%) but absence (0%) in the puppies with tumor metastasis suggested the importance of antibodies in resistance to metastasis.