The objective of this study was to investigate the antimicrobial activities of saturated fatty acids and fatty amines against methicillin-resistant Staphylococcus aureus (MRSA). The antimicrobial activity of saturated fatty acids and fatty amines was determined by oxygen meters with multi-channels and disposable oxygen electrode sensors (DOX-96). Lauric acid, the most effective among the saturated fatty acids, showed antimicrobial activity at 400 microg/ml against methicillin-susceptible Staphylococcus aureus (MSSA) and MRSA. The minimal inhibitory concentration (MIC) of fatty amines depended on each hydrophobic chain length. The MIC of myristylamine was 1.56 microg/ml; most effective of the fatty amines. In time-kill curves, lauric acid and myristylamine produced a bactericidal effect and a bacteriostatic effect at 4-fold the MIC, respectively. The antimicrobial activities of lauric acid and myristylamine were decreased by human plasma. Cytotoxicity of 3 saturated fatty acids and 3 fatty amines was examined in cultured endothelial cells. Although cytotoxicity of fatty amines was severer than that of saturated fatty acids, myristylamine showed the highest value of apparent therapeutic index among them. DOX-96 was useful for screening antimicrobial substances, especially in the case of insoluble substances. We found that myristylamine showed anti-MRSA activity comparable to that of vancomycin and teicoplanin.