Here we have shown that tonic mIgM-containing BCRs of primary human B cells are apparently organized as monomers and dimers within the plasma membrane of resting cells, whereas a CLL-derived chronic BCR tends to be organized as dimers and oligomers, which is dependent on the presence of an intact recognition motif within the Ig heavy chain V region of the CLL-derived BCR. Here, BCR is linked to B-cell chronic lymphocytic leukemia.