Kv1.3 channels regulate proliferation of normal lymphocytes, but the role of voltage-gated potassium channels in transformed hematopoietic cells is not known. We examined transcripts for Kv1.3, h-erg, h-eag, and BEC1 genes in primary lymphocytes and leukemias and in several hematopoietic cell lines. Surprisingly, BEC1, formerly thought to be brain-specific, was present in all the primary leukemias examined, in resting peripheral blood lymphocytes, and in proliferating activated tonsillar cells, lymphocytes from Sjö gren's patients, and Epstein-Barr virus-transformed B-cells. Only h-erg mRNA was up-regulated in the cancer cells, but this was not due to proliferation per se, because it was not elevated in any of the proliferating noncancerous lymphocyte types examined. Nor did h-erg transcript levels correlate with the B-cell subset, because it was elevated in immature neoplastic B-CLL cells (CD5 ؉ ) and in a CD5