Over a time period of five years leukemic blast samples from 141 consecutive patients with adult ALL were referred to our laboratory, for molecular evaluation of chromosome abnormalities. The t(9;22), t(4;11) and t(1;19) which are most commonly found in adult ALL with a B-precursor phenotype were molecularly analyzed by similar RT-PCR based protocols. BCR-ABL transcripts generated by the t(9;22) translocation were demonstrated in 36 patients (25%) and were restricted to the 109 patients with B precursor ALL (33% of this group). Of 83 patients showing a, common phenotype (CD10+), 34 were BCR-ABL positive (41%) whereas only 2 out of 26 with Null ALL (HLADr+, CD19+, CD10) were positive. Interestingly, the percent of BCR-ABL positive CD1O+ ALL increases significantly with age being 20% in patients less than 30 years old and more than 50% in older patients. None of the T-ALL (24 patients) and B-ALL (8 patients) were positive. The majority of cases (67%) showed the p190 gene subtype. The cytogenetic diagnosis of Philadelphia chromosome was always confirmed by the molecular analysis and this approach allowed for the detection of the presence of the BCR-ABL rearrangement in 26 patients when a negative result or no metaphases were obtained. The complete remission rate was similar among BCR-ABL positive and negative patients but a shorter remission duration was observed in those showing molecular evidence of t(9;22) and this finding was significantly evident in CD1O+ ALL patients. By means of comparison, in most of the same adult ALL patients, we analyzed the yet unrecognized prevalence of the t(4;11) and t(1;19) translocations by the molecular analysis of their chromosomal breakpoints. Rearrangements of the ALL-1 gene on 11q23 band and ALL- l1AF.4 fusion transcripts specific for the t(4;11) were demonstrated in 7 out of the 21 Null ALL investigated, with no additional positive cases found among the other ALL subgroups. Overall the clinical behavior of t(4; 11) positive patients was dismal with a very short CR duration. Chimeric E2A-PBX1 transcripts generated by the t(1;19) were found in only two of the 87 B-precursor ALL analyzed. The presented results provide further evidence for the utility of RT-PCR based methods for the molecular diagnosis of chromosome translocations in ALL. The identification of such abnormalities can significantly contribute to the identification of more appropriate therapeutic options for standard and high risk ALL patients