The effects of piroxicam, tenoxicam, diclofenac sodium, acetylsalicylic acid and tiaprofenic acid on the chemotaxis and random migration of human polymorphonuclear leukocytes were investigated, using zymosan-activated serum as chemo-attractant, with a modified Boyden chamber technique. All five compounds significantly reduced chemotaxis. The random migration of polymorphonuclear leukocytes was inhibited by piroxicam, diclofenac sodium and tiaprofenic acid but not by tenoxicam or acetylsalicylic acid. The inhibitory effect of these non-steroidal anti-inflammatory drugs on polymorphonuclear leukocyte chemotaxis and on random migration was generally dose-dependent. The results suggest that the drugs studied may have a direct effect on polymorphonuclear leukocyte chemotaxis and that this activity may contribute to their anti-inflammatory properties.