The present study characterizes the effect of two nitric oxide (NO) donors, S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP), on the ability of neutrophils to perform different responses triggered by immune complexes (IC). Pretreatment of neutrophils with either GSNO or SNP exerted a biphasic action on antibody-dependent cellular cytotoxicity (ADCC) performed against erythrocytes (E) coated with IgG antibodies (IgG-E), depending on the amount of IgG employed. While with high amounts of antibodies ADCC was markedly inhibited, at low amounts of antibodies it was significantly increased. Both effects were prevented by haemoglobin, a NO scavenger. Moreover, these effects were reproduced by the cell-permeable analogue of cGMP, dibutyryl cGMP (Bt2cGMP). Other neutrophil functions triggered by IgG-E were also examined. It was found that NO donors did not affect either the phagocytosis of IgG-E or the emission of chemiluminescence (CL). Finally, neutrophil functions triggered by soluble IC (sIC) and precipitating IC (pIC) were analysed. It was observed that NO donors did not modify either cytotoxicity performed towards non-sensitized target cells or CL emission. The significance of these results is discussed.