The chromosomal banding patterns of canine transmissible sarcoma (CTS) cells were analyzed and compared to those of normal canine cells with four banding techniques. In addition, N-myc and N-ras oncogenes on the chromosomes of the CTS cells were investigated by the in situ hybridization method. The modal chromosome number of the CTS cells was 58:17 metacentrics and 41 acrocentrics. Based on their G- and Q-banding patterns most of the chromosomes of the CTS cells were present in normal cells except for the second largest metacentric chromosomes. It was considered that the metacentric chromosomes of the CTS cells results from Robertsonian translocation of normal chromosomes. The long arm of the second largest metacentric element of the CTS cells was stained negatively by the Q-banding technique. The C-band was found on the long arm of the second largest metacentric element and three pairs of N-bands were recognized in the same region. It was suggested that this amplification of N-bands enhanced tumorigenic properties in the CTS. No N-myc or N-ras oncogenes were detected on chromosomes of the CTS cells by the in situ hybridization method.