Abnormal trafficking of chronic lymphocytic leukemia (CLL) cells may account for the differences in accumulation of malignant lymphocytes within the bone marrow and lymphoid tissues of this lymphoproliferative disorder. We therefore hypothesized that CLL cells aberrantly express one or more receptors involved in lymphocyte trafficking. Leukemia cells from patients with B-cell CLL showed no quantitative difference in surface expression of L-selectin, LFA-1, or CD44 by flow cytometry compared to normal B cells. Analysis of L-selectin by dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot, however, demonstrated a consistent, reproducible approximately 3.7 kDa decrease in the M(r) of L-selectin on CLL cells compared to normal B cells. In contrast, Western blot analysis revealed no obvious qualitative abnormality in either CD11a (the alpha-chain of LFA-1) or CD44 on CLL cells. Analysis of L-selectin cDNA by polymerase chain reaction revealed identically sized products for both normal and CLL cells, suggesting that the abnormality in M(r) does not result from a difference in primary structure. Inhibition of N-linked glycosylation by tunicamycin resulted in the production of identical-sized nascent L-selectin by normal and CLL cells. These studies demonstrate that L-selectin on CLL cells is aberrantly glycosylated compared to normal peripheral blood lymphocytes. The functional importance of this aberrant glycosylation is unclear, however, since L-selectin is shed normally from phorbol myristate acetate (PMA)-stimulated CLL cells and since normal and CLL lymphocytes bind equally well in vitro to high endothelial venules. Understanding the mechanism that accounts for the aberrance may provide important insights into the molecular basis of CLL.