Our previous studies of a translocated c-myc gene in the Raji Burkitt's lymphoma cell showed somatic mutations in exons 1 and 2. We have extended these observations to two other translocated c-myc genes and find a common occurrence of mutation in the noncoding exon 1. We also found that in Raji cells, unlike other Burkitt's lymphoma cell lines, the normal allele of the c-myc gene is transcribed as well as the translocated gene. These results support a model in which c-myc oncogene activation in Burkitt's lymphoma occurs by disruption of a normal transcriptional control mechanism in which the c-myc protein is itself involved.