The objective of the present study was to investigate the effects of saponin fraction from anomalous fruits of Gleditsia sinensis (SFGS) on picryl chloride-induced delayed type hypersensitivity (PC-DTH) and functions of T lymphocytes and macrophages in mice. SFGS (100, 200 mg/kg), orally administered during either sensitization stage or effector stage, produced remarkable inhibition of PC-DTH. In vitro, SFGS (1, 2, 4 microg/ml) concentration-dependently attenuated concanavalin A (Con A)-elicited mouse splenocyte proliferation and interleukin 2 (IL-2) production. At concentrations of 10 and 20 microg/ml, SFGS inhibited lipopolysaccharide (LPS)-induced production of nitric oxide and interleukin 1beta (IL-1beta) of mouse peritoneal macrophages. The findings indicate that SFGS attenuates PC-DTH in mice, which is probably mediated by preventing proliferation and differentiation of T cells during the sensitization stage and suppressing activation of macrophages during the effector stage.