Intracellular and serum activities of aldolase (ALS) were biochemically determined in lymphocyte subpopulations from normal subjects and patients with B-chronic lymphocytic leukemia (B-CLL). Aldolase activity was significantly lower in T cells of CLL than in normal T cells (2.9 +/- 1.5 vs. 4.7 +/- 2.1 Sigma Units (SU)/6 x 10(6) cells, p < 0.05). The aldolase activity also was significantly (p < 0.001) lower (3.1 +/- 1.9 SU/6 x 10(6) cells) in CLL B lymphocytes than in normal B lymphocytes (18.1 +/- 6.5 SU/6 x 10(6) cells). Moreover, the serum levels of ALS in all patients with B-CLL were higher than that in normal subjects (8.1 +/- 5.8 vs. 2.2 +/- 0.8 SU/ml, p < 0.02). Our findings demonstrate that T lymphocytes from patients with B-CLL display enzyme activity different from that of normal T cells. This may reflect the abnormal maturity of the residual T cell population in B-CLL.