Molecular studies have recently demonstrated that the E2A transcription factor gene was consistently located on chromosome 19 at the breakpoint of the 1;19(q23;p13) translocation, which characterizes a number of leukemias harboring a pre-B cell phenotype. Using a specific E2A gene probe spanning the DNA binding and dimerization domain obtained by PCR methodology, we were able to detect the rearrangement of the E2A gene in four cases (three patients and one cell line) of pre-B acute lymphoblastic leukemia with t(1;19) translocation.