Current dogma holds that non-steroidal anti-inflammatory drugs (NSAIDs) act by inhibition of the synthesis and release of prostaglandins. However, NSAIDs also inhibit the activation of neutrophils, which provoke inflammation by releasing products other than prostaglandins. We now report that NSAIDs (for example, indomethacin, piroxicam) inhibit activation of neutrophils by inflammatory stimuli such as C5-derived peptides and leukotriene B4 even when cyclooxygenase products generated in suspensions of stimulated neutrophils (prostaglandin E and thromboxanes) are present. Sodium salicylate (3mM) greatly inhibited aggregation of neutrophils but had no effect on aggregation of platelets or production of thromboxane induced by arachidonate. Sodium salicylate and other NSAIDs also inhibit calcium movements (45Ca uptake, changes in fluorescence of chlortetracycline and Quin-2). Aspirin, sodium salicylate, indomethacin, and piroxicam also enhanced the post-stimulation rise in intracellular cyclic AMP. NSAIDs therefore inhibit early steps in neutrophil enhance intracellular levels of cyclic AMP.