It is well known that cadmium (Cd) has toxic and carcinogenic effects in rodents and humans, but the effects of Cd on apoptosis are still not clear. Although some studies have shown that Cd has apoptotic potential, other studies have shown that Cd can be antiapoptotic. Parameters such as sensitivity of the exposed organism or cells and the exposure conditions should be important in delineating the effect of Cd on apoptosis. In the present study, we aimed to determine the apoptotic index (AI) of Sprague-Dawley rat tissues that are loaded at a lower Cd concentration than the critical concentration (50 mu g/g) for its toxic effects. Metallothionein (NIT) levels of tissues were also determined and the experiments repeated with copper (Cu)-exposed rats. We detected decreases in the apoptotic index in liver and lung tissues of Cd-exposed groups accompanied with an increase in MT levels. Also, decreases of Al were detected in the liver tissues of Cu-exposed groups. These findings indicate that Cd can suppress apoptosis in vivo. The possible role of NIT expression on the suppression of apoptosis and the importance of free-Cd ion concentration on switching antiapoptotic effects to proapoptotic effects are also discussed.