In contrast to IgG Fc receptor II (Fc gamma RIIa), the function of Src-family kinases, Syk and phosphoinositide 3-kinase (PI3K) in signal transduction of glycosylphosphatidylinositol-anchored Fc gamma RIIIb has not been analyzed in detail. Therefore pharmacological inhibitors were used to define the role of specific kinases in signalling of Fc gamma RIIa and Fc gamma RIIIb in myeloid cells. We demonstrate that the broad tyrosine kinase inhibitor genistein, the Src-family kinase inhibitor PP2, and the Syk kinase inhibitor piceatannol inhibit [Ca2+]i rise induced by both low-affinity Fc gamma R in neutrophils. Genistein and PP2 additionally prevent Fc gamma R-triggered hydrogen peroxide generation. In contrast, wortmannin, a PI3K inhibitor, which blocks Fc gamma RIIIb activation completely, abolishes Fc gamma RIIa-mediated [Ca2+]i flux only in the beginning. In addition, herbimycin A, a further specific inhibitor of Src-family kinases leads to a delayed Fc gamma RIIa-induced [Ca2+]i rise in THP-1 cells. In summary, our data demonstrate differences between both low-affinity IgG Fc receptors, and provide evidence for an essential role of Src-family kinases, Syk and PI3K in Fc gamma RIIIb-mediated signalling.