A new series of benzoxazinone analogs were designed, synthesized, and assayed to determine their effects on superoxide anion generation and neutrophil elastase (NE) release in formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-activated human neutrophils. Of these, compounds 6-10 showed a potent dual inhibitory effect on NE release and superoxide anion generation. In contrast, compounds 11-15 exhibited highly selective and potent inhibitory activities on NE release. These results indicate that the inhibitory activity on NE release in FMLP-activated human neutrophils depended on the position of chloro-substituent in the A ring. On the other hand, 13 significantly attenuated the increase in myeloperoxidase (MPO) activity and edema in the lung of rats after trauma-hemorrhagic shock. Therefore, these compounds could be developed as new NE inhibitors.