In B-chronic lymphoproliferative disorders (B-CLD) adhesion molecules (AM) have been investigated in order to explain the variable biologic behavior and dissemination patterns and to assess their contribution to the differential diagnosis and prognosis of these diseases. The main AM studied either by immunohistochemistry on lymph node sections or by flow cytometry in blood and bone marrow specimens are L-selectin, CD11a/CD18 (LFA-1), CD54 (ICAM-1), CD44 (HCAM), CD11c/CD18 (gp150/95), and CD49d/CD29 (VLA-4). Among B-CLD, hairy-cell leukemia (HCL) and follicular lymphoma (FL) show a uniform AM expression pattern. Thus, HCL is characterized by high CD54, CD44, VLA-4, CD11c, and CD18 and by low or absent CD11a and L-selectin, whereas FL confined to the lymph nodes is characterized by high CD11a, CD18, and CD54 expression. Diffuse growth and dissemination of FL is associated with alteration in the AM profile. Mantle-cell lymphoma (MCL) seems to be characterized by low or absent L-selectin and CD11c and high CD54 expression, especially compared with B-chronic lymphocytic leukemia (B-CLL). B-CLL is the most heterogeneous among all B-CLD with respect to AM expression. In general, low LFA-1 and CD54, high L-selectin and CD44, and variable CD11c characterize B-CLL. Cases with splenomegaly as their prominent feature bear high CD11a, CD18, CD29, and CD11c on the surface of the leukemic cells. Small lymphocytic lymphoma (SLL) shares the same AM phenotype with B-CLL, with the possible exception of LFA-1, which is strongly expressed on SLL cells. LFA-1 and CD54 are more frequently positive in lymphoplasmacytic lymphoma (LPL) as compared with B-CLL. Splenic lymphoma with villous lymphocytes differs from B-CLL by its high LFA-1, VLA-4, and CD54 and low L-selectin expression, whereas its high LFA-1 positivity can differentiate it from HCL. Surface and soluble AM have been investigated as possible prognostic markers in these diseases. Conflicting data exist concerning the prognostic significance of surface AM. However, high soluble (s)CD44 and CD54 levels in B-CLL and non-Hodgkin's lymphomas (NHL) are considered as adverse prognostic factors.