The heterogeneity of 5'-nucleotidase activity in lymphoblasts of acute lymphoblastic leukemia, demonstrated by an improved cytochemical method.

5'-Nucleotidase activity was demonstrated in the cell membrane of normal and leukemic lymphocytic cells by an improved cytochemical method. In the normal blood lymphocytes an average percentage of 20.6 +/- 2.9 5-nucleotidase positive (5 N +) cells were found. Among the various cases investigated, in 12 "null"-acute lymphoblastic leukemias an increased percentage of 5 N + blast cells was observed (33.4 +/- 27.95%). The heterogeneity however of the individual percentage of 5 N + blasts of each case in this group, was remarkable (0-89%) and not readily explicable. We also found a considerable percentage of 5 N + circulating lymphoma cells in patients with leukemic nodular poorly differentiated lymphocytic lymphoma (18.5 +/- 9.9%). In contrast, a low percentage of 5 N + leukemic cells was observed in the B and T chronic lymphocytic leukemia, B and T prolymphocytic leukemia, hairy cell leukemia and T acute lymphoblastic leukemia.