Physiological factors involved in immunity and tissue repair with regulate homeostasis, a physiological function of the connective tissue, are as yet unidentified. We earlier detected the granulation-promoting action of carnosine, and reported on the acceleration of tissue repair in experimental as well as clinical studies. In that study, immunoregulatory effects of carnosine and beta-alanine were examined by the plaque-forming cell (PFC) count and delayed hypersensitivity reaction (DHR). The PFC value increased in mice pretreated with these agents. In these mice, PFC reaction to 2 X 10(7) SRBC was enhanced but that to 1 X 10(9) SRBC was suppressed. The agents also suppressed excess immunoreaction in immature mice but increased weakened immunoreaction in aged animals. Furthermore, the agents had the optimal doses for the enhancement of both PFC reaction to 1 X 10(8) SRBC and DHR to 1% picryl chloride. They also induced recovery of immunofunction suppressed by the administration of MMC. Carnosine and beta-alanine exerts immunoregulatory effects by activating both T and B cells. Our observations indicated that the agents not only promote tissue repair but also help maintain homeostasis and accelerate spontaneous healing.