A human-mouse myeloma analogue termed HMMA2.11TG/O was constructed by fusion of the mouse myeloma cell line P3x63Ag8.653, a mutant derivative of MOPC21, with bone marrow mononuclear cells from a patients with IgA myeloma. The HMMA2.11TG/O cell line is resistant to 6-thioguanine and ouabain and sensitive to HAT. The cell line secretes no detectable immunoglobulin and has a hybrid karyotype and cell surface phenotype. An average fusion efficiency for growth of hybridomas of 1/17,000 fused cells was obtained in fusions with human peripheral blood mononuclear cells (PBM), Pokeweed Mitogen (PWM) stimulated PBM, and Epstein-Barr Virus (EBV) transformed polyclonal B cell lines. Over 75% of hybrids secrete detectable immunoglobulin and the cloning efficiency of the hybrids at 1 cell/well averages 25%. Antibody secreting cloned hybridoma cell lines were obtained by fusion directly with PBM from an immunized volunteer and by fusion with in vitro, secondarily immunized, EBV transformed polyclonal cell lines. Five hybridomas secreting human monoclonal IgM anti-tetanus antibodies and 2 secreting human monoclonal IgG anti-tetanus antibodies were selected and cloned from 6 fusions performed specifically for anti-tetanus antibody. Immunoglobulin and antibody secretion by cloned hybrids has been stable for 5-10 months at present. Immunoglobulin and antibody secretion in routine cultures passaged every 3-4 days has been 8-42 micrograms/ml. This human-mouse myeloma analogue should prove useful for the routine production of human monoclonal antibodies.