The activities of the key glycolytic enzymes phosphofructokinase (PFK), pyruvate kinase (PK) and hexokinase in addition to adenosine deaminase, purine nucleoside phosphorylase (PNP) and lactate dehy-drogenase (LDH) have been measured in lymphocytes from 39 cases with B-chronic lymphocytic leukaemia (B-CLL). According to the percentage of circulating large non-granular atypical lymphocytes (AL) the B-CLL cases were classified as: typical ( < 10% of AL; 28 cases) and atypical (10-25% AL; 11 cases). In both groups the median lymphocyte volume (MLV) was assessed and correlated with the correspondent enzyme activities.The MLV of B-CLL lymphocytes was significantly (p < 0.001) decreased (149.9 ± 19.4 fl) as compared to normal B lymphocytes (175.1 + 14.5 fl) and it was significantly (p < 0.001) lower in typical B-CLL (141.8 ± 12.2 fl) than in atypical B-CLL (172.0 ± 17.2 fl). Furthermore, in patients with typical B-CLL, all enzyme activities when expressed as U/109 cells were, with the exception of PFK, significantly decreased compared to normal B lymphocytes. However, when the results were expressed as U/ml cells, only PK, PNP and LDH remained significantly low.These findings demonstrate that the determination of MLV in addition to morphology may be a useful tool to distinguish the two previously described morphological B-CLL variants (typical and atypical) and that these two different B-CLL groups are also distinguishable on the basis of three enzyme activities, PK, PNP and LDH which have been shown to be less dependent on cell size than the other enzymes, also studied here.