The electrochemical behavior of aluminum in isotonic saline solutions, citrated human plasma, and citrated human blood is studied using potentiostatic and potentiodynamic polarization techniques complemented with scanning electron microscopy (SEM) and dispersive x-ray analysis. The effect of corrosion products on plasmatic proteins is investigated using electron microprobe analysis and immunoelectrophoresis analysis. Electrochemical data show a breakdown of the protective film on aluminium, due to the action of chloride, leading to the pitting of the metal. During pitting, the interaction of aluminium ion and the plasma proteins produces a nonadherent precipitate. Strong protein denaturation can be observed by immunoelectrophoresis of the precipitate suspended in physiologic solutions. The convenience of using organic fluids in addition to saline solutions to evaluate in vitro the behavior of metal for implants is suggested.