A QSAR study using the novel hydrophobic descriptor (logPmw), which is a descriptor for membrane affinity, of our fibrinogen inhibitors FK633 (1), FR158999 (21), and related derivatives was performed, and resulted in good correlation (n = 19, s = 0.268, F = 6.38**, r = 0.667). Based on these results, we constructed a hypothesis by which these potent inhibitors bind to the receptor via the biomembrane and the C-terminal moiety functions as an anchor moiety.