Two novel cell lines, PC-53 and PC-53A were established from an adult ALL patient, at third relapse and in the terminal accelerated phase respectively. Both lines displayed the phenotype of B-cell precursors (CD19+, CD38+, CD20-, cytoplasmic-mu-, immunoglobulin gene rearrangement), identical to the freshly isolated blast cells. Chromosomal analysis showed a prominent 45-XX karyotype, including three marker chromosomes. No chromosome 8 abnormalities were detectable, consistently with a non-rearranged c-myc locus. Both cell lines were EBV-negative. Growth stimulation by autologous supernatant was observed for PC-53 cells during the first 4 months in culture, whereas it was much less evident for PC-53A cells. Thus, PC-53 and PC-53A cells represent a useful tool to investigate the mechanisms involved in the clonal expansion of B-cell precursors.