The results of the present study indicate that TREM-1 can be used as marker of bacterial infection in patients with lung infiltrates. sTREM-1, nTREM-1, mTREM-1 and CRP were comparable to their discriminating ability between a pulmonary infiltrate of infectious origin and a pulmonary infiltrate of non-infectious origin. sTREM-1 levels were decreased within the first 48 hours in patients with CAP with favourable outcome probably after the initiation of appropriate therapy followed by improvement of clinical symptoms. Finally, sTREM-1 levels above 180 pg/ml were an accurate independent predictor of in-hospital mortality from CAP.