Delayed-type hypersensitivity reaction (DTH) to TNCB in TNCB-primed mice was increased when mice was treated with sodium selenite. In vitro studies showed that primed T cells proliferated more vigorously when TNP-conjugated spleen adherent cells (SAC) from Se-treated mice were the stimulators as compared with SAC of untreated controls. TNP-conjugated SAC treated in vitro with sodium selenite were even stronger stimulators than SAC treated in vitro. The results indicate that Se enhances DTH by promoting antigen presentation.