This study was undertaken to investigate the eftects of Cd administered ad libitum for 6 weeks on the cellular immune responses of Balb/c mice. The results were summarized as follows; 1. The mice fed 25, 50 and 100ppm Cd drank as much as control, but the mice fed 200ppm Cd drank significantly less water after Cd exposure than did control. Increasing rates of body weight of Cd-fed mice for 6 weeks were as this, control group 27.0%, Cd administered groups(25, 50, 100 and 200ppm) 28.54%, 28.31%, 20.49% and 18.04%, respectively. 2. Absolute spleen to body weight(mg/g) of control, 25, 50, 100 and 200ppm Cd administered groups were $4.34{\pm}0.23$, $4.20{\pm}0.54$, $4.80{\pm}0.87$, $4.25{\pm}0.32$ and $4.40{\pm}0.32$, respectively. Splenic cellularity(${\times}10^7$) of control was $24.29{\pm}5.98$ but increased to $27.72{\pm}5.48$, $32.96{\pm}8.44$, $28.32{\pm}8.76$ and $29.64{\pm}4.08$ in 25, 50, 100 and 200ppm Cd-fed groups, respectively. 3. Total $CD_4{^+}$ cells(${\times}10^7$) of control, 25, 50, 100 and 200ppm Cd-fed groups were $9.15{\pm}2.24$, $10.40{\pm}2.04$, $12.04{\pm}3.08$, $10.20{\pm}3.16$ and $10.80{\pm}1.48$, respectively and total $CD_8{^+}$ cells(${\times}10^7$) of these groups were $2.32{\pm}0.56$, $2.54{\pm}0.27$, $3.12{\pm}0.80$, $2.25{\pm}0.70$ and $2.24{\pm}0.28$, in order. On the other hand, $CD_4{^+}/CD_8{^+}$ ratios in total cells were increased significantly except for 50ppm Cd-fed group($3.88{\pm}0.01$). And that of control was $3.97{\pm}0.02$, but those of 25, 100 and 200ppm were $4.35{\pm}0.01$, $4.54{\pm}0.03$ and $4.81{\pm}0.03$. 4. Phagocytosis rates of peritoneal macrophages were increased significantly in 25 and 50ppm Cd groups($36.34{\pm}9.45$ and $37.15{\pm}9.22$, respectively), but 100 and 200ppm groups showed similar rates($18.20{\pm}3.04$ and $19.48{\pm}3.22$ respectively) to that of control($21.43{\pm}3.62$). 5. In mitogen-induced splenocyte proliferation, various concentraions of $CdCl_2(10^{-4}-10^{-7}M)$ were added to mitogen-stimulated culture in vitro. Splenocyte proliferation induced by LPS was decreased dose dependently, but proliferation by Con-A was increased slightly in concentrations of $10^{-7}-10^{-6}M$. 6. Significant cytotoxicity of splenocytes with $CdCl_2$ were shown at $10^{-4}M$ treated group, especially at 24 hrs. From these results, it could be concluded that Cd might modulate the immune responses by modifying a distribution of T cell subpopulations.