Lactate dehydrogenase (LDH) and enzyme-linked immunosorbent assay (ELISA) have attracted much attention recently for the evaluation of blood compatibility of biomaterials due to their convenience and quantifiability. In this paper, the use of LDH and ELISA is described for in situ investigation of platelet behavior on biomaterial surfaces, including quantification of platelet adhesion and platelet activation, after suitable testing conditions have been established. The material samples investigated in these tests included low temperature isotropic carbon (LTIC), Ti-O films, and phosphorus- and aluminum-doped TiO2 films. The evaluation results show that the lowest platelet adhesion and activation are observed on phosphorus-doped TiO2 films while the highest platelet adhesion and activation are observed on LTIC. In addition, conventional platelet adhesion experiments were performed for comparison, and yielding similar evaluation results as LDH and ELISA. It is suggested that LDH and ELISA tests can be successfully applied to evaluate the blood compatibility of biomaterials and can show many advantages, such as quantification, reliability and objectivity, compared with conventional platelet adhesion test.