Background The immunomodulatory effects of glucocorticoids (GCs) have been described as bimodal. High concentration of GCs exerts immunosuppressive effects and low levels of GCs are immunopermissive. While the immunosuppressive mechanisms of GCs have been investigated intensely, the immunopermissive effects of GCs remain unclear. A lot of studies showed GCs could exert rapid non-genomic actions. We herein studied the rapid immunopromoting effects of GCs.Methods We observed the rapid (within 30 minutes) effects of corticosterone on respiratory burst of mouse peritoneal macrophages and studied their mechanisms. The superoxide anions were measured by cytochrome C reduction assay.Protein kinase C phosphorylation was measured by West blotting and membrane fluidity was evaluated by fluorescence polarization measurement.Results The 10-8 mol/L and 10-7 mol/L corticosterone rapidly increased the superoxide anions production by macrophages, which were insensitive to GC-receptor antagonist, mifepristone, and protein-synthesis inhibitor,cycloheximide. Corticosterone coupled to bovine serum albumin was able to mimic the effects of corticosterone. The effects were independent of protein kinase C pathway and the change in membrane fluidity.Conclusions The results indicate that corticosterone rapidly promote the superoxide anions production by mouse peritoneal macrophages may through non-genomic mechanisms. This study may contribute to understanding the effects of GCs under stress condition and the physiological significance of nongenomic effects of GCs.