Hypokalemia due to renal potassium loss has frequently been observed in patients with acute myeloid leukemia (AML). The pathogenic mechanism for this hyperkaluresis is unclear. In this report we describe a patient with AML FAB M4, in whom the clinical course, the electrolyte disturbances, the serum aldosterone levels, and the diffuse hyperplasia of the adrenal cortex documented a typical case of marked secondary hyperaldosteronism. On analysis of the leukemic cells of this patient compared with normal bone marrow cells, a significant increase of renin-like activity in the cytosol of the blast cells was noted. Activation of the renin-angiotensin-aldosterone system by paraneoplastic production of renin-like activity in AML blast cells might contribute to the hypokalemia often observed in patients with acute myeloid leukemia.