Characterization of a membrane-IgM-negative variant cell line derived from the murine B-cell line 38C-13 revealed the absence of light chains and the presence of polypeptides with an apparent molecular size of 18 kDa and 14 kDa, previously denoted omega and iota and characteristic of pre-B cells. These polypeptides assemble with the mu chains into complexes with apparent molecular sizes of about 100 kDa and 200 kDa. It has been previously shown that light-chain-deficient variants of the 38C cell line undergo 'secondary' light chain rearrangements. It is suggested, therefore, that complexes of mu and the 'surrogate' light chains omega and iota play a role in this process. As these complexes do not reach the cell surface we would like to propose that the mechanism of secondary rearrangement is intracellularly controlled.