Bactericidal ability of polymorphonuclear leukocytes (PMNL) is impaired in chronic renal failure (CRF). This function of PMNL is mediated by the generation of oxidizing radicals and the latter event requires O2 consumption by these cells. The present study examined both basal and FMLP-stimulated rise in cytosolic calcium ([Ca2+]i) and O2 consumption of PMNL from normal subjects and hemodialysis patients and from CRF rats, and evaluated the potential role of secondary hyperparathyroidism of CRF on these properties of PMNL. Basal levels of [Ca2+]i were significantly higher, and FMLP-induced increments in [Ca2+]i were significantly lower in PMNL of both humans and rats with CRF than in normals. Basal and FMLP-stimulated O2 consumption were significantly lower in CRF subjects and rats than in normals. These derangements were prevented by prior parathyroidectomy of CRF rats or by their treatment with verapamil from day one of CRF. Also, therapy of rats with pre-existing CRF with this drug reversed the abnormalities in [Ca2+]i and in O2 consumption of PMNL. The data indicate that: (1) CRF is associated with derangements in the homeostasis of [Ca2+]i of PMNL and their oxygen consumption, (2) these abnormalities are, most likely, mediated by the state of secondary hyperparathyroidism of CRF, and (3) verapamil, which blocks the PTH-induced entry of calcium into cells, and prevents as well as reverses these PMNL dysfunctions. These results implicate the excess PTH of CRF in the genesis of the defective bactericidal function of PMNL, and assign a new dimension to PTH toxicity in CRF.