A 72-year-old man presented with a left testicular tumor and underwent orchiectomy. The tumor was massively infiltrated with myeloma cells bearing monoclonal cytoplasmic IgD lambda. Three months after orchiectomy, he developed huge abdominal masses and subsequently ascites containing numerous myeloma cells. An IgD-secreting myeloma cell line, designated delta-47, was established from the ascites. This cell line expressed CD4 and CD38, but lacked Fc and complement receptors, surface immunoglobulin, CD19, HLA-DR, and PCA-1. CD30 was detected on the cultured cells but not on the ascites tumor cells. Delta-47 cells secreted the same immunoglobulin (IgD lambda) as was found in the patient's serum. The light chain had a molecular weight of 35 kD which was larger than that of the normal light chain. Chromosome analysis of delta-47 revealed an aneuploid karyotype with complex abnormalities including 1q+, 2p+, and 14q+. To our knowledge, this is the only IgD-secreting myeloma cell line and would provide a useful tool for the study of IgD production and IgD myeloma.