Gynostemma pentaphyllum Makino (GP) is a herbal tea widely grown in Southeast Asia. However, this herbal tea can be contaminated with some heavy metals, especially cadmium (Cd), from agricultural areas, which may affect human health. The objective of this study is to evaluate the immunomodulatory effects of Cd contaminated in GP herbal tea and inorganic Cd on rat splenocytes. Rats were divided into groups and treated with drinking water (control), high CdCl 2 in drinking water (HCd; 0.05 mg/L), GP herbal tea containing 0.05 mg/L Cd (GP-HCd) for 4 months, low CdCl 2 in drinking water (LCd; 0.006 mg/L), and GP herbal tea containing 0.006 mg/L Cd (GP-LCd) for 6 months. After the treatments, Cd accumulation in organs and blood was detected by using a graphite furnace atomic absorption spectrophotometer. In spleen, HCd-treated rats had 4-fold higher Cd accumulations than GP-HCd-treated rats. Cd accumulation in liver and kidney in the HCd group also increased significantly. There were no significant changes in total leucocyte and lymphocyte counts; however, these parameters tended to decrease slightly in LCd, GP-LCd, and GP-HCd groups. The HCd group (ex vivo) significantly produced suppressive effects on T cell mitogen-induced splenocyte proliferation, with 1 mug/mL Con A and PHA-P. In addition, 0.5 mug/mL PWM-induced B cell proliferation, through T cell functions, was also significantly inhibited by HCd as compared to the control group, while GP-HCd had no effects. However, both GP-LCd- and LCd-treated rats had a slight increase in Con A-stimulated splenocyte proliferation. This study indicated that high Cd contamination in drinking water alone had suppressive effects on T cell functions, but these effects could not be found with the same Cd level contamination in GP herbal tea.