Serum secretory component level in myeloma patients with disorders of the secretory surface.

Secretory component (SC) in myeloma serum was measured by a double antibody radioimmunoassay. It was elevated in patients with IgA myeloma and the highest level was observed in a patient with macroglobulinemia. The presence of disorders of secretory surface in myeloma patients slightly but not significantly elevated the serum SC concentration. A significant correlation between serum SC and IgG is demonstrated, but not between serum SC and IgA. Over the whole patient groups, serum SC is significantly related to serum IgM but not when patients with macroglobulinemia are excluded from the calculation. Serum SC is present as SC-IgM in macroglobulinemia and SC-IgM and SC-IgA in IgA myeloma.