The effect of combined antibiotic and corticosteroid treatment on the course of haematogenously acquired Staphylococcus aureus nephritis was studied. Mice were given a single injection of S. aureus producing toxic shock syndrome toxin-1 in a dose capable of inducing a high frequency of inflammatory kidney lesions and divided into three groups according to a treatment regimen. In all untreated animals inflammatory infiltrates were seen in kidney cortex and medulla with high frequencies of glomerular (90%) and tubular damage (50%) as well as fibrotic changes (50%). The treatment with antibiotics alone reduced significantly only the occurrence of focal inflammatory infiltrates. In contrast, the mice treated with a combination of antibiotics and corticosteroids displayed in 64% of cases normal histological kidney appearance and a significant decrease in occurrence of glomerular (P<0.01) and tubular (P<0.05) lesions. Immunohistochemically, the combined treatment resulted in a more pronounced decrease in numbers of CD4, IL-2R (four to fivefold) and CD8 positive cells in kidney inflammatory lesions compared to antibiotics only treated group. Thus, glucocorticoids in association with antibiotics are shown to improve the outcome of septic murine nephritis, possibly due to suppression of kidney infiltrating T cells.