The steady-state level of c-myc proto-oncogene mRNA was investigated in the EBV-negative human B-lymphoma line BJAB and 2 sublines that have been converted by EBV into stable EBV-genome-carrying and EBNA-positive status. The EBV-converted sublines expressed c-myc at a 2- to 6-fold higher level than the original BJAB during exponential growth. The EBV-positive BJAB lines are known to differ from the parent line in several phenotypic characteristics, including increased agarose clonability, lower serum requirement and, in one case, increased tumorigenicity in nude mice. The pattern of increased c-myc expression accompanying EBV conversion was not observed in the myc/Ig translocation-carrying Burkitt lymphoma line RAMOS or in 2 of its EBV-converted sublines.