A 'B' cell line, originating from a patient with chronic myeloid leukemia and containing the Philadelphia chromosome, was established after Epstein-Barr virus transformation. The Philadelphia chromosome was the sole chromosomal abnormality in this line, designated as PhB1 cell line. In DNA hybridization studies we detected rearrangements in the bcr gene and in the immunoglobulin heavy chain joining region. The phenotypes of the cells were typical of mature B cells expressing antigens CD19, CD20, CD22, CD23, CD39, HLADR, IgM, and kappa. The expression of the 210 bcr-abl chimeric protein was detected by means of an immunoprecipitate assay.