To review and summarize literature regarding stimulatory and inhibitory signaling pathways from different types of Fc gamma receptors (FcgammaRs).Articles were obtained from Medline from January 1991 to April 2002.Over 100 English language papers and reviews published over the last 11 years were selected.Stimulatory Fcgamma receptors include FcgammaRI, FcgammaRIIA, FcgammaRIIC, and FcgammaRIII A. They transduce signals through the immunoreceptor tyrosine-based activation motif (ITAM) in subunits or in the cytoplasmic domain. Inhibitory Fcgamma receptors, such as FcgammaRIIB, are single chain receptors, transducing signals through an immunoreceptor tyrosine-based inhibitory motif (ITIM) in cytoplasmic domains. Stimulatory signals include protein phosphorylation, increase in intracellular free calcium, the production of 1,4,5-triphosphate inositol (IP(3)) and diacylglycerol (DAG) mainly through the Src-family kinases, phosphoinositide 3-kinase (PI3-K) and phospholipase C (PLC). Inhibitory signaling has been implicated in the repression of the above activities as well as inhibition of B cell responses through Src homology 2-containing inositol phosphatase (SHIP).