Female ICR mice were administered with bovine colostrum and were treated with cyclophosphamide to establish immunosuppressed status. The cytokine levels in sera and splenocyte culture supernatants and splenic T cell subpopulations were determined. Bovine colostrum substantially restored the percentage of the total T cell population (CD3+) and effector CD4+ T lymphocyte, as well as influencing the CD4:CD8 ratio in the spleen. It was effective in increasing the concentrations of interleukin (IL)-2, interferon-?, granulocyte-macrophage colony-stimulating factor and decreasing the levels of IL-6 in vivo and in vitro. The levels of IL-10 in splenocyte culture supernatants were increased, whereas the levels of IL-4 in splenocyte culture supernatants were dramatically decreased. Moreover, bovine colostrum was efficacious in enhancing the production of IL-1a in vitro. Thus, bovine colostrum could exhibit immunoregulatory effects via modulating splenic T lymphocytes subpopulations. Bovine colostrum may have pleiotropic effects on the production of cytokines in vivo and in vitro.