The aim of the present study is to analyze the relationship between serum immunoglobulin (Ig) levels and the immunological phenotype and the clinicohaematological features of B-cell chronic lymphocytic leukaemia (B-CLL) in a series of 126 patients. Eighty-eight of the cases (70%) had a decreased concentration of at least one Ig. IgM and IgA were the most frequently decreased (60% and 49% respectively). A serum monoclonal gammapathy was found in 4 patients, Ig M/k in two cases and IgM/l and IgG/k in one case. Patients with hypogammaglobulinaemia had a similar surface phenotype as patients with normal Ig levels (MRFC+, sIg+, CD20+, HLA/DR+, FMC7-, CD5+, CD9+). On the other hand the cases with hypogammaglobulinaemia displayed the features of a more advanced disease, a higher incidence of organomegalies (p less than 0.05), anaemia and/or thrombopenia (p less than 0.05), a diffuse bone marrow pattern (p less than 0.05), advanced clinical stages (p less than 0.05) as well as higher levels of both peripherial blood (p less than 0.02) and bone marrow lymphocytosis (p less than 0.02). These findings suggest that the presence of hypogammaglobulinaemia in B-cell patients is probably more related to a higher tumor burden than to either certain stages of B-cell differentiation or a particular cellular phenotype.