Dexamethasone administration has been widely used as a model of immunosuppression in various species. The objective of the work reported here was to evaluate immune function in pigs treated with dexamethasone. Experiment 1 pigs were assigned to either control (n = 10) or 2 mg/kg dexamethasone (n = 10) treated groups. Treatments were administered 48 and 24 h before immune function testing. The dexamethasone-treated pigs received the drug on 22 of 72 experimental days. Pigs in experiment 2 were assigned to one of three groups: control (n = 10), 2 mg/kg dexamethasone (n = 10), or 6 mg/kg dexamethasone (n = 10). Treatments were given once and immune functions were evaluated 3 and 27 h after treatment. Lymphocyte blastogenesis, total and differential white blood cell count, and several measures of in vitro neutrophil function were measured in both experiments. Antigen specific antibody production, growth rate, and organ weights at necropsy were also measured in experiment 1. There were no consistent changes in neutrophil functions in these experiments. Lymphocyte blastogenesis to concanavalin A and pokeweed mitogen was significantly (p <0.05) enhanced during experiment 1 in dexamethasone-treated pigs; antigen specific antibody production was not altered by treatment. Dexamethasone treatment (both 2 and 6 mg/kg) in experiment 2 caused a profound (p <0.02−0.01) decrease in lymphocyte blastogenesis to all three mitogens tested at 3 h after treatment. Lymphocyte proliferation returned to control levels by 27 h after treatment in experiment 2. Dexamethasone treatment was also associated with a relative neutrophilia and lymphopenia in both experiments. Dexamethasone-treated pigs in experiment 1 grew slower, had larger livers and kidneys , but smaller spleens than control animals. The transient decrease in lymphocyte blastoenesis lack of consistent , changes in neutrophil function, and unaltered antibody production despite treatment with large doses of dexamethasone indicate that pigs are remarkably resistant to immunosuppression by this drug.