Two classes of agents have effects on the chemotactic response of human neutrophils. Chemoattractants such as activated complement components, E. coli culture filtrates (BF) and the recently discovered N-formylmethionyl peptides, initiate directed movement, whereas chemotactic modulators enhance or depress cell movement initiated by chemoattractants. We and others have previously shown that cyclic AMP (cAMP) depresses neutrophil migration toward BF whereas cyclic GMP (cGMP) enhances the same process. In the present study, we examined the effects of several chemoattractants and chemotactic modulators on neutrophil levels of cGMP and cAMP. Trypsinized human complement, the E. coli BF and the synthetic peptide, formylmethionylalanine stimulated the accumulation of neutrophil cGMP (40 to 70% average increase) but had little effect on cAMP concentrations. The enhancing chemotactic modulators — phenylephrine, prostaglandin F2α, carbachol, and phorbol myristate acetate — also produced small (19 to 34%) but significant increases in PMN cGMP levels. In contrast, two agents which inhibit the chemotactic response, isoproterenol and prostaglandin E1, significantly elevated cAMP concentrations in PMN. These results suggest that the ability to elevate cGMP is inherent in the action of both chemoattractants and enhancing chemotactic modulators. Increases in cAMP appear to be correlated with inhibition of chemotaxis.