A progressive inhibition of both antibody-dependent cellular cytotoxicity (ADCC) and Fc gamma R expression was observed when peripheral blood mononuclear cells (PBMC) were incubated with soluble immune complexes (IC) at 37 degrees. Treatment of these IC-blocked PBMC with normal human serum (NHS) reversed both effects and increased the release of attached IC from the cell surface when compared to heat-inactivated serum (HI-NHS) or culture medium (TCM) treatments. Immunofluorescence studies demonstrated a redistribution of IC, predominantly in the form of caps in IC-blocked cells treated with HI-NHS (56%) or TCM (51%). However, when these IC-blocked cells were treated with NHS, only 11% of them showed caps redistribution. We propose that NHS regulation of Fc gamma R expression may be a physiological way of modulating the different immunological events triggered by IC.