The immunomodulatory activity of HN-02, an extract containing a mixture of andrographolides (i.e., andrographolide [88 +/- 5 %] plus 14-deoxyandrographolide and 14-deoxy-11,12-didehydroandrographolide together [12 +/- 3 %]) in a pure powder form was evaluated at 1.0, 1.5, and 2.5 mg/kg on different in vivo and in vitro experimental models. In a delayed-type hypersensitivity (DTH) mouse model, potentiation of the DTH reaction was observed after treatment with cyclophosphamide (CYP) and HN-02 individually. However, CYP potentiation of the DTH reaction was reversed by HN-02 pretreatment. Furthermore, HN-02 treatment elevated the depressed hemagglutination antibody (HA) titer and increased the number of plaque-forming cells (PFCs) in the spleen cells of mice that had been treated with CYP and challenged with sheep red blood cells (SRBC). Further, it was also found that HN-02 treatment stimulated phagocytosis in mice. A significant increase in total WBC count and relative weight of spleen and thymus was observed in mice during 30 days of treatment with HN-02. The present experimental findings demonstrate that HN-02 has the ability to enhance immune function, possibly through modulation of immune responses altered during antigen interaction, and to reverse the immunosuppression induced by CYP.