The transforming genes of retroviruses (v-onc) are derived from normal cellular genes referred to as proto-oncogenes. These cellular genes have the capacity for conversion to oncogenes (c-onc) that are capable of inducing or maintaining the transformed state when they are overly expressed or altered by mutation or rearrangement. To study the possible involvement of these genes in human leukemia, we have analyzed their expression in a variety of fresh samples. We found that a number of oncogenes are expressed in different leukemic types and that although the transcript size did not vary for each gene, the copy number did. The myc gene (2.4 kb transcript) and the rasHa gene (1.5 kb transcript) were universally expressed. But in contrast to rasHa, the myc signal intensity varied. Myb (4.5 kb transcript) was expressed in all samples except B cell diseases. We detected low levels of abl expression (multiple mRNA species) in all leukemic types analyzed. Sis gene (4.2 kb transcript) expression was restricted to one patient sample with chronic myelogenous leukemia in blast transformation.