We recently reported that the widely distributed neuropeptide vasoactive intestinal peptide (VIP) reduces inflammatory lung injury due to a variety of agents and inhibits the associated generation of cyclo-oxygenase and lipoxygenase products. We therefore investigated whether VIP may inhibit phospholipase A2 activity, thus reducing the release of arachidonic acid, the common precursor of all eicosanoids. VIP dose-dependently inhibited PLA2 of porcine pancreas and of Naja naja venom, as assessed by the release of free [3H]oleic acid from labeled Escherichia coli phospholipids. The potency of VIP was similar to that of mepacrine, with 50% inhibition at 400-500 microM. The closely related peptide helodermin produced 50% inhibition at 200 microM, but secretin and peptide histidine isoleucineamide produced little or no inhibition. The results suggest that VIP and helodermin selectively inhibit PLA2 in vitro. If this activity is exerted in vivo, it may contribute to the anti-inflammatory activity of these two peptides.