To explore the hypothesis that protein adsorption followed by platelet adhesion and activation has an effect on the nature of the subsequent inflammatory response, we studied the cell-implant reactions to Ti and Au in blood and the peritoneal cavity. The metals were exposed to blood (in vitro) and peritoneal fluid (in vivo). In blood the adhesion and activation of platelets and leucocytes were studied by fluorescence microscopy using specific FITC-labeled antibodies or acridine orange. Intraperitoneal leucocyte adhesion was studied by scanning electron microscopy, transmission microscopy, or by staining with acridine orange. The metallic surfaces were exposed to both blood and peritoneal fluid for times varying from 15 s to 4 h. The results show (a) that a significantly larger number of platelets followed by a correspondingly large number of leucocytes initially adhere to Ti rather than to Au, (b) that the rate of the inflammatory response as manifested by the appearance of leucocytes is more rapid in the peritoneal cavity than in blood, and (c) that cells attach directly to the Au surfaces while being separated by an amorphous layer on the Ti surfaces. Thus an interesting nexus exists between the composition of the adsorbed protein layer, platelet adsorption, and activation and the rate and nature of leucocyte recruitment and interaction with implanted materials.