Two chimeric genes, PML-RARa and RARa-PML, are formed as a consequence of the acute promyelocytic leukemia (APL)-specific reciprocal tranlocation of chromosomes 15 and 17 [t(15;17)]. PML-RARa is expressed as a fusion protein. We investigated the organization and expression pattern of the RARa-PML gene in a series of APL patients representative of the molecular heterogeneity of the t(15;17) and found (i) two types of RARa-PML mRNA junctions (RARa exon 2/PML exon 4 or RARa exon 2/PML exon 7) that maintain the RARa and PML longest open reading frames aligned and are the result of chromosome 15 breaking at two different sites; and (us) 10 different RARe-PML fusion transcripts that differ for the assembly of their PML coding exons. A RARa-PML transcript was present in most, but not all, APL patients.