AbstractThe synthesis of surface immunoglobulin by chronic lymphocytic leukemia cells was studied in short‐term culture using radioactive amino acids and sugars. The membranal location of the nascent immunoglobulin was evidenced by the difference in the electrophoretic pattern of the membranal and cytoplasmic proteins, and by the absence of nascent surface immunoglobulin in cultures containing chain‐specific antibody. The nascent surface immunoglobulins comprised 7 S IgM and a large excess of free light chains of lambda type. Anti‐ü‐chain serum blocked the nascence of membranal IgM, while λ‐type as well as K‐type anti‐L‐chain sera blocked the nascence of both membranal IgM and free light chains. Radioactive glucosamine and mannose were not incorporated into the nascent surface immunoglobulin. There was no secretion of nascent proteins into t