The immunomodulatory properties of a diterpene lactone andrographolide and Kan Jang--a standardized fixed combination of Andrographis paniculata extract SHA-10 and Eleutherococcus senticosus extract SHE-3 were investigated. Their role on spontaneous and phytohemagglutinin (PHA)-induced proliferation of human peripheral blood lymphocytes (PBL) and on production of interferon-gamma (INF-gamma) and tumor necrosis factor-alpha (TNF-alpha) were determined in vitro. Proliferation of PBL induced by PHA was enhanced by co stimulation with andrographolide and Kan Jang. At the same time andrographolide and Kan Jang inhibit spontaneous proliferation of PBL in vitro. These preparations also have effect on the formation of INF-gamma, TNF-alpha and some immune activation markers such as neopterin (Neo), beta-2-microglobulin (beta2MG), and soluble receptor for interleukin-2 (sIL-2R or sCD25) in blood cells culture. Andrographolide and Kan Jang stimulate the INF-gamma, Neopterin and beta2MG formation, but do not have any significant effect on the production of INF-gamma and Neopterin in PHA stimulated blood cells. An opposite effect on these immune makers was observed in the PHA-stimulated blood cells: both andrographolide and Kan Jang increase the formation of TNF-alpha and beta2MG in cultivated whole blood cells. Thus, andrographolide and Kan Jang can have an in vitro effect on the activation and proliferation of immunocompetent cells as well on the production of key cytokines and immune activation markers. The results show an overall higher effect of the fixed combination as compared with the equivalent amount of the pure substance andrographolide. The data are consistent with results from clinical studies of Kan Jang and contributed to a better understanding of these results.