Modulation of immune responses is highly relevant in tumor cell destruction. The present study is focused on the effect of Andrographis paniculata extract (APE) and its isolated compound andrographolide (ANDLE) on cell-mediated immune responses in normal and tumor-bearing control animals. Treatment with APE and ANDLE significantly enhanced natural killer cell activity in normal (APE, 46.82% cell lysis; ANDLE, 40.79% cell lysis) and tumor-bearing animals (APE, 48.66% cell lysis; ANDLE, 42.19% cell lysis) on the fifth day, and it was observed earlier than in tumor-bearing control animals (12.89% cell lysis on day 9). Antibody-dependent cellular cytotoxicity was also increased in APE (45.17% cell lysis on day 11) as well as ANDLE (39.92% cell lysis on day 11)-treated normal and tumor-bearing animals (APE, 47.39% cell lysis; ANDLE, 41.48% cell lysis on day 11) compared to untreated tumor-bearing control animals (maximum of 11.76% cell lysis on day 17). An early enhancement of antibody-dependent complement-mediated cytotoxicity was also observed by the administration of APE and ANDLE in normal as well as tumor-bearing animals. APE and ANDLE administration could significantly enhance the mitogen-induced proliferation of splenocyte, thymocyte, and bone marrow cells. Moreover, treatment of APE and ANDLE significantly elevated the production of interleukin-2 and interferon-gamma in normal and Ehrlich ascites carcinoma-bearing animals.