An Epstein-Barr virus (EBV)-negative lymphoma line (JBL) was established in vitro from pleural effusion of an EBV-seropositive 29-year-old Japanese female with Burkitt's lymphoma. JBL cells as well as her original lymphoma cells bore monoclonal surface IgM with lambda light chains. The JBL line grew in single cell suspension with a doubling time of 30 hours. Attempts were made to serially transplant JBL cells in antilymphocyte serum-treated newborn hamsters; intraperitoneal implantation of 1-3 X 10(7) cells gave rise to invasive tumors in all recipients with death after 10 to 14 days. The hamster-passage line, now in the 9th passage, has been converted to an ascitic form with progression to leukemia in some animals. A "starry sky" pattern closely resembling the human tumor material was preserved in every tumor through serial animal passage.