Pericentric inversion of chromosome 16, translocation (16;16) and del(16q), resulting in a chimerical fusion of CBFbeta and MYH11 genes, are typically seen in the M4Eo French-American-British (FAB) classification subset of acute myelogenous leukemia (AML). In this study, we analyzed 70 cases of acute non-lymphoblastic leukemia, mainly of the M4 or M5 type. We report the very unusual presence of the t(16;16) and CBFbeta/MYH11 fusion transcript in an M7 patient. Ten M4Eo and four non-M4Eo patients presented an inv(16), t(16;16) or CBFbeta/MYH11 fusion transcript. In most cases, the common 'A-type' CBFbeta/MYH11 fusion transcript was detected. In addition to the eight different breakpoints and the three alternative splicing variants already described, evidence of a new CBFbeta/MYH11 fusion transcript was found which involves a 785-bp deletion of MYH11. Moreover, two patients had an unusual transcript, to our knowledge only observed once. Only one patient had abnormal eosinophilic differentiation without chromosome 16 cytogenetic abnormalities or detectable CBFbeta/MYH11 fusion. Conversely, only one patient presented CBFbeta/MYH11 fusion without abnormal eosinophilic differentiation. Altogether, our data suggest a correlation between the CBFbeta/MYH11 fusion transcript and characteristic abnormal eosinophilic differentiation, whatever the FAB subtype or the percentage of abnormal eosinophils