The present study was done to examine the involvement of protein kinase C and protein tyrosine kinase in intracellular Ca²⁺ mobilization in C5a-stimulated neutrophils. Although protein kinase C inhibitors, staurosporine and H-7 inhibited intracellular Ca²⁺ release in C5a-stimulated neutrophils, they did not affect Ca²⁺ influx across the plasma membrane and elevation of [Ca²⁺]_i C5a-induced intracellular Ca²⁺ release and Ca²⁺ influx were inhibited by protein tyrosine kinase inhibitors, genistein and methyl-2,5-dihydroxycinnamate. ADP-evoked elevation of [Ca²⁺]_i was inhibited by genistein and methyl-2,5-dihydroxycinnamate but was not affectd by staurosporine and H-7. Genistein and methyl-2,5-dihydroxycinnamate reduced the store-regulated Ca²⁺ influx in thapsigargin-treated neutrophils, while the effect of staurosporine and H-7 was not detected. When neutrophils were preincubated wih phorbol 12-myristate 13-acetate, the stimulatory effect of C5a on the elevation of [Ca²⁺]_i was reduced. These results suggest that protein tyrosine kinase may be involved in control of intracellular Ca²⁺ release and Ca²⁺ influx across the plasma membrane in C5a-activated neutrophils.