The effects of 1-(5-isoquinoline sulphonyl)-2-methyl piperazine (H-7), a recently described inhibitor of Ca2+/phospholipid-dependent protein kinase (protein kinase C), were studied during under-agarose migration of human polymorphonuclear neutrophils (PMN) stimulated by various chemoattractants, in order to determine whether protein kinase C is involved in PMN locomotion. The effect of H-7 on the oxidative burst induced by phorbol 12-myristate 13-acetate or N-formyl-methionyl-leucyl-phenylalanine (FMLP) was also measured. Pre-incubation of PMN with H-7 concentrations ranging from 50 to 400 microM inhibited: (i) spontaneous PMN migration under agarose; (ii) the directed migration induced by activated serum, leukotriene B4 or FMLP; and (iii) the speed of the migration induced by FMLP. The inhibition by H-7 of FMLP-induced directed migration was less when FMLP was used at high concentrations which, in the absence of H-7, inhibit locomotion. H-7 depressed the oxidative burst induced by phorbol myristate acetate (PMA) but not that induced by FMLP. All the effects of H-7 on the oxidative burst and migration were reversed by washing PMN after H-7 treatment. These findings indicate that protein kinase C, inhibitable by H-7, is involved in a mechanism controlling the speed of PMN locomotion.