A cultured cell line, P30/Ohkubo with pre-T cell phenotype, was established from an 11-year-old girl with acute lymphoblastic leukemia (ALL). According to the morphological, cytochemical and immunological analyses, P30/Ohkubo was found to have common-ALL antigen, Ia-like antigen, pan-T cell antigen, and L2 morphology with localized acid phosphatase staining, but not rosette-forming capacity with sheep erythrocytes, B1 antigen or surface immunoglobulins. Chromosome analysis revealed that P30/Ohkubo had two constant marker chromosomes [11q +, del (9)], but lacked 14q +. These findings indicate that P30/Ohkubo is a novel cultured cell line of pre-T cell phenotype. These characteristics have remained unchanged for more than 20 months since establishment of the cell line.