A human myeloma cell line designated LOPRA-1 has been established from ascites fluid containing malignant plasma cells of a patient with IgA2/kappa multiple myeloma. The cultured cells which are Epstein-Barr virus (EBV) negative have retained the morphological, cytochemical, ultrastructural and immunophenotypical features of well-differentiated plasma cells. They express the plasma cell antigen PCA-1, the antigens CD28 (Kolt-2) and CD38 (OKT10), the transferrin-receptor (OKT9), and some epitopes of the CD24 antigen (HB8, VIB E3), but are negative for surface immunoglobulins. HLA class II antigens (HLA-DP, -DQ, -DR) and other B-cell markers such as CD10 (CALLA), CD19 (B4), CD20 (B1), CD21 (B2), CD22 (HD39), CD23 (MHM6), CD37 (BL14) and CD39 (G28-8) as analysed by both flow cytometry and immunocytochemistry (PAP/APAAP). With respect to immunoglobulin synthesis, two stable clones were selected by single cell cloning: clone LOPRA-1/5 synthesizes large amounts of alpha 2 heavy and kappa light chains, but secretes only small amounts of these molecules, whereas clone LOPRA-1/4 is clearly devoid of intracellular immunoglobulin heavy and light chains and thus appears to be a chain loss variant. Cytogenetic analysis revealed a pseudotriploid phenotype with several structurally abnormal marker chromosomes: 3n + -, 70, XX, -X, -1, -4, -6, -8, -8, -13, -16, +7, +18, +21, +i(1q), +i(1q), +6q-, +3mar.