Parathyroidectomy is proposed to be protective against gentamicin nephrotoxicity in rats. In the present study, we evaluated the effects of bovine PTH(1-34) on gentamicin accumulation in cultured kidney epithelial cell lines, oppossum kidney (OK) cells which possess PTH receptors and LLC-PK1 cells which are devoid of PTH receptors. Ten days after seeding, the culture medium was exchanged for medium containing 1 m M gentamicin and bovine PTH. The cell gentamicin concentration was measured by a substrate-labeled fluorescence immunoassay (TDA gentamicin kit). Gentamicin uptake was accelerated by bovine PTH in OK cells but not in LLC-PK1 cells. The enhancing effect of bovine PTH seems to be mediated by a cAMP-dependent process. The results suggest that PTH accelerates gentamicin accumulation in renal tissues and potentiates gentamicin nephrotoxicity.