Burkitt lymphomas contain reciprocal translocations between chromosome 8 and one of the chromosomes containing the immunoglobulin gene loci, prompting speculation that consequent activation of a crucial gene(s) on chromosome 8 might be involved in the generation of these tumors. Recently the human counterparts of the retroviral oncogenes v-myc and v-mos have been mapped to chromosome 8. We have, therefore, analyzed the level of transcription of the cellular myc and mos genes in a variety of undifferentiated B cell lymphomas of Burkitt and non-Burkitt type that possess either an 8;14 or an 8;22 translocation. These lines expressed 2- to 5-fold more myc-specific RNA than do B cell lines without a translocation. Tumor cell lines of American origin with an 8;14 or 8;22 translocation expressed similar amounts of myc-specific RNA. Tumor cell lines of African origin contained slightly higher levels of myc-specific RNA than did those of American origin. However, level of expression does not appear to correlate with the presence or absence of Epstein-Barr virus. Therefore, a major increase in the transcription of this gene secondary to translocation is unlikely to be the cause of Burkitt lymphoma. There was no evidence of mos-related transcripts in any of the cell lines tested.