Serum β2-microglobulin (β2M) was measured in 22 patients with B chronic lymphocytic leukemia (CLL) and in 15 healthy age-matched control subjects. The patients were allocated in stages in accordance with the Rai and Binet systems. The β2M mean value in the CLL group was significantly higher than in the control group. There was a positive correlation between β2M and the clinical stage in both staging systems. The mean serum levels of β2M in stages A, B and C of Binet’s system showed statistical differences while in stage A they did not differ from those found in the control group. No correlation was demonstrated between β2M and the peripheral lymphocyte concentration. A slight correlation was found between β2M and the degree of bone marrow lymphocyte infiltration, whereas a stronger relationship was observed when the type of infiltration (non-diffuse versus diffuse) was considered. Patients with bulky disease had mean β2M values much higher than the others.