In the present paper, we are reviewing experimental evidence demonstrating that phagocytic cells, such as macrophages, may be used as a biomarker of immunotoxicity in wildlife studies. We will first present data obtained after exposure in vitro with selected chemicals showing the comparative sensitivity of phagocytic cells from different species. These results demonstrate that, at least for metals, each species produce a similar shaped dose-response curve, although considerate interspecies sensitivity is evident. These results also demonstrate the sensitivity of the phagocytic activity, suggesting indeed that this function could be used to monitor exposure to chemicals. The similar shaped dose-response curves imply that mechanisms of action may also be similar. Furthermore, based on the relative speices sensitivity, sentinel species could be selected for field monitoring. Such an approach may also be useful to establish correction factors required to extrapolate results between species. This sensitivity of the phagocytic activity of macrophages will be further under controlled conditions in laboratory animal models. Finally, the reliability of this approach will be demonstrated using case studies with wildlife species.