Membrane potential is involved in the regulation of several immune functions developed by granulocytes. The Na(+)/K(+) gradient across the plasma membrane, mainly generated by the Na(+)/K(+) pump, plays a key role in the maintenance of membrane potential. This study is focused on the correlation between plasma membrane potential and the in vitro receptor - triggered respiratory burst of normal human peripheral granulocytes. The respiratory burst was measured as superoxide anion release by the cytochrome c reduction test and plasma membrane potential was modulated by experimental changes of the extracellular potassium concentration. Results show a differentiated cellular response, depending on the in vivo activation state and on the signals received in vitro by granulocytes via CR3 or FcgammaR. Alteration of the membrane potassium gradient modulates the respiratory burst of unstimulated and CR3-activated cells, whilst it does not seem to significantly interfere with the signals delivered by FcgammaR.