MINEGISHI, M., TSUCHIYA, S., MINEGISHI, N. and KONNO, T. Establishment of Five Human Malignant Non-T Lymphoid Cell Lines and Mixed Lymphocyte-Tumor Reaction. Tohoku J. exp. Med., 1987, 151(3), 283-292-Five human malignant non-T lymphoid cell lines have been established. THP-4 and THP-7 were derived from two children with common type acute lymphoblastic leukemia (ALL), THP-6 and THP-8 from two children with null cell type ALL and THP-9 from a child with malignant lymphoma. THP-4 was positive for cytoplasmic μ, B4, common ALL antigen (CALLA) and Ia-like antigen (Ia), THP-7 positive for B4, CALLA and Ia, THP-8 positive for B4 and Ia, and THP-9 positive for surface μ-λ, B1, B4, CALLA and Ia. No antigenic determinants for monoclonal antibodies used were detected on THP-6. THP-4, THP-7, THP-8 and THP-9 were able to stimulate allogeneic lymphocytes vigorously. THP-6 without Ia stimulated not only allogeneic lymphocytes, but also autologous ones. THP-7 did not stimulate autologous lymphocytes.