Poly(A)-polymerase enzymic activity was biochemically determined in lymphocytic extracts from 40 patients with chronic lymphocytic leukemia of the B cell type. The enzymic activities of patients with stage A, B and C disease were (U/mg of protein): 4.9 +/- 5.5, 12.5 +/- 7.5 and 20.9 +/- 18.9, respectively. The difference in the enzyme level between stage A and C patients was statistically significant (p less than 0.05). Comparison of the enzyme activity level in relation to the pattern of bone marrow involvement revealed that patients with a diffuse pattern of infiltration had a significantly higher enzyme level (17.9 +/- 15.5 U/mg of protein) than patients with interstitial or mixed infiltration patterns (5.9 +/- 6.6 and 7.9 +/- 7.0 U/mg of protein; p less than 0.025). Finally, patients who required treatment for their disease also had a significantly higher poly(A)-polymerase activity level (14.5 +/- 13.9 U/mg of protein) than patients with stable disease (4.9 +/- 5.5 U/mg of protein; p less than 0.05). Our results indicate that the enzyme poly(A)-polymerase may be used as a biological marker in patients with chronic lymphocytic leukemia.