Hyperosmolality in renal medulla inhibits functions of polymorphonuclear leukocyte (PMN) such as phagocytosis, intracellular killing, and superoxide generation. The main factors of hyperosmolality in the renal medulla are thought to be urea and NaCl. We studied the luminol-dependent chemiluminescence (CL) response of PMNs to three different stimulators: phorbol myristate acetate (PMA), formyl-methionyl-leucyl-phenylalanine (FMLP), and opsonized zymosan (OZ). When PMNs were incubated or preincubated with hyperosmotic urea or NaCl solutions, CL responses were significantly reduced following stimulation by each of PMA, FMLP, or OZ. Reduction of CL response was concentration and osmolality dependent in hyperosmotic urea and NaCl solution. These results suggest that respiratory burst and production of active oxygen species of PMNs through three different signal transduction pathways are inhibited in hyperosomotic conditions comparable to the renal medulla.