In spite of the great interest in developing a perfluorocarbon (PFC) blood substitute with a wide range of applications, the in vivo and in vitro knowledge of the interactions between PFCs and cells, from the ultrastructural point of view is limited up to now. In this framework, our observation confirmed the PFC particle uptake by rat hepatocytes in vivo as well as in vitro. The absence of endocytosis by rat and guinea pig myocytes in vivo, to be confirmed by in vitro experiments, could favour a safe use of PFCs as components of cardioplegic solutions.