The changes of pulmonary platelet trapping (PPT) were observed in dogs after they were traumatized with steel-sphere shooting and then the therapeutic effects of nalorphine were studied.It was found that the PPT rate was significantly increased in the 8th hour after injury;when nalorphine was administered before and after gunshot wounding,the PPT rate of the traumatized dogs was signficantly lowered.The fact indicates that the increase of PPT rate in the gunshot dogs results from the activation of opiate ? receptor in the lungs.