This study set out to determine the immunomodulatory effects of a health food high-peptide meal in immunodeficient mice that was induced by either hydrocortisone (HY) or cyclophosphamide (CP). Five separate trials were performed in which animals were randomly divided into 5 groups of 12 mice for each experimental trial. Group 1 served as the vehicle control. Animals assigned to groups 3-5 (dose groups), were each administered once daily with 1.67, 3.33 or 6.67 g kg(-1) body weight of a high-peptide meal, respectively, for 30 consecutive days. Animals from groups 2 to 5 that were included in trials 1 to 4, each received an intramuscular administration of HY at 40 mg kg(-1) body weight on days 22, 24, 26, 28, 30. Animals from groups 2-5, in trial 5, each received an intraperitoneal administration of CP at 50 mg kg(-1) body weight, on days 26 and 27. On day 31, all groups of mice were differentially screened for immunomodulatory activity following the conclusion of the above experiments. In HY-treated mice, the high-peptide meal accelerated the recovery of the phagocytic function of both macrophages and the reticuloendothelial system, and restored NK cell activity. In CP-treated mice, the high-peptide meal promoted a humoral immune response to sheep red blood cells (SRBCs). These results demonstrated the immunomodulatory effects of a high-peptide meal.