Sairei-to (TJ114), a 12-component Japanese herbal medicine, is used to treat immune-related diseases. We investigated the effects of oral administration of TJ114 in a murine model of cardiac transplantation with fully mismatched allografts. Untreated CBA mice rejected C57BL/6 hearts acutely (median survival time [MST], 7 days), whereas survival of allografts from mice given TJ114 was significantly prolonged (MST >100 days). Secondary CBA recipients of C57BL/6 hearts also had prolonged allograft survival (MST >100 days) after adoptive transfer of whole or CD4 splenocytes from primary CBA allograft recipients given TJ114. None of the individual components of TJ114 prolonged allograft survival, suggesting that its effects require administration of the combination agent. In mixed leukocyte cultures, proliferation of splenocytes from TJ114-treated CBA recipients was markedly suppressed compared with that of splenocytes from untreated mice, and interferon-gamma production was significantly reduced. Thus, in our model, TJ114 treatment induced hyporesponsiveness to cardiac allografts and generated CD4 regulatory cells.