We have studied the expression of the three human acute myeloid leukemia (AML) genes in primary samples of non-Hodgkin's B-cell lymphomas in which translocations involving these loci were not present. We found a widespread expression of the three AML genes in all the lymphoma samples as well as in the purified normal B-lymphocytes. Thus, the presence of the three mRNAs "per se" does not allow the identification of the pathological status. However, AML1 showed a different transcription pattern in the neoplastic tissues with respect to the normal B-cells. The AML1b isoform proved to be peculiar to this lymphoma. Our data support the idea that qualitative and quantitative alterations of AML1 gene expression deriving from deregulating mechanisms other than translocations may be involved in this malignancy. The usage of two differently regulated promoters driving the expression of the transcripts AML1b and AML1c may be one of these mechanisms. Finally, we report the presence of a new alternatively spliced transcript in normal B-cells.