Neutrophil homogenates contained a high affinity guanosine triphosphatase (GTPase) that was stimulatable (+27%) by the addition of 100 nM N-formyl chemotactic peptide (CHO-pep), but not by 1 microgram X ml-1 phorbolmyristate acetate (PMA). Kinetic analysis of the stimulation demonstrated an apparent lagtime of 14.3 +/- 6.9 s between the addition of CHO-pep and the optimal GTPase stimulation. The GTPase activity (but not CHO-pep-stimulated GTPase activity) was preserved in a highly purified plasma membrane fraction of the homogenate. From these observations we suggest that both a high affinity guanine nucleotide binding protein and GTPase are closely associated with the plasma membrane CHO-pep receptor. The possibility that GTPase activity may influence guanine nucleotide regulation of adenylate cyclase during CHO-pep stimulation of neutrophils is discussed.