Neutrophil receptor(s) for neutrophil activating peptides 1 and 2 were studied by competition binding experiments with radiolabeled NAP-1 and NAP-2 preparations. NAP-1 bound with one affinity, NAP-2 with two quite different affinities, to common receptor(s) on neutrophils. Concentrations of NAP-2 needed to induce exocytosis of beta-glucosaminidase corresponded to the higher dissociation constant of the two binding equilibria. Thus, the binding of NAP-2 to PMN with high affinity does not activate the cells.