The "constitutive" expression of the c-myc gene was detected in leukemia cells obtained from 4 patients with an acute myeloid leukemia, 3 with chronic myeloid leukemia and 1 with a myelodysplastic syndrome. Studies were undertaken to determine whether or not the myc gene was rearranged or mutated in exon I within a 3'Pvu II region, a transcriptional attenuation site. Studies to explore the possibility of a point mutation in the N-ras gene were also conducted. No abnormalities were detected in either gene. Studies should be undertaken evaluating the possibility of a post-transcriptional mechanism, such as alteration of RNA stability, which could be responsible for the constitutive expression of c-myc gene.