A continuous lymphoblastoid cell line was established from a JMV tumor transplant related to Marek's disease (MD). It is designated RPL1 (JMV) lymphoblastoid cell line. This cell line contains DNA sequences complementary to MD virus DNA and has an antigen similar to MD-tumor-associated surface antigen (MATSA). However, it lacks any MD virus (MDV) rescuable in vivo or in vitro. The cell line has surface antigens typical of chicken thymus cells (T cells) and histocompatability antigens different from those of the host chicken.