1. Adhesion of neutrophils (PMNs) to vascular endothelial cells (EC) is a critical step in recruitment and infiltration of leukocytes into tissues during inflammation. Substance P (SP), a neuropeptide released from sensory nerves, evoked PMN adhesion to EC. The NK receptor subtype(s) and the cell type(s) involved were investigated. 2. SP was coincubated with human PMNs and EC from the human umbilical vein (HUVEC); adhesion was quantitated by computerised microimaging fluorescence analysis. 3. The proadhesive effects of SP (range 10(-18)-10(-6) M) were illustrated in a biphasic dose-response curve, with a maximum at 10(-15) M (276+/-16% adhesion vs control; P<0.01) and another one at 10(-10) M (200+/-18% adhesion vs control; P<0.01). Neurokinin A was less active and neurokinin B was inactive. The adhesion molecules LFA-1 and OKM-1, but not selectins, were involved according to results with selective mAbs. 4. The NK(1) agonist [Sar(9),Met(O(2))(11)]SP reproduced the effects of SP, whereas the NK(2) agonist [betaAla(8)]-neurokininA (4-10) acted at 10(-13)-10(-8) M only. The NK(3) agonist, senktide, was ineffective. 5. The NK(1) antagonists, CP 96,345 and L 703,606 (both 10(-6) M), abolished the effect of 10(-15) M SP and inhibited that of 10(-10) M SP by 56+/-5% (P<0.01). By comparison, the NK(2) antagonist, SR 48,968 (10(-7) M), partially antagonised the adhesion evoked by 10(-10) M SP (% inhibition: 61+/-6; P<0.05). 6. Since preincubation of PMNs and HUVEC with SP gave the same results it is clear that both cell types contributed to its proadhesive effects. 7. These results indicate that SP induced a proadhesive effect during inflammatory processes, which was mediated by NK(1) and NK(2) receptors.