Soluble triggering receptor expressed on myeloid cells is upregulated on the surface of inflammatory cells in the presence of bacterial infections apparently excluding those due to Mycobacterium tuberculosis. Therefore, sputum concentrations of Soluble Triggering Receptor Expressed on Myeloid Cells (s-TREM-1) may be of value in distinguishing bacterial pneumonia from pulmonary tuberculosis (PTB) in patients with respiratory infections. The current pilot study was designed to evaluate whether s-TREM-1 concentrations measured in the sputum of patients with suspected community-acquired pneumonia (CAP) allowed differentiation of those patients with PTB from other causes of pneumonia and to correlate s-TREM-1 with the CURB-65, a marker of disease severity. Methods. Soluble s-TREM-1 concentrations were measured in sputum samples from patients admitted to a tertiary hospital with CAP or PTB by means of an ELISA procedure. Results. Soluble-TREM-1 was readily detectable and quantifiable in sputum samples from patients with both CAP and PTB, with concentrations of 234 ± 47 and 178 ± 36 pg/ml respectively, but did not differ significantly between the 2 groups. However, patients with PTB had significantly lower leukocyte counts, 9 ± 1.3 versus 15 ± 1.4 x 109/l compared to those without PTB. Interestingly, sputum s-TREM-1 concentrations correlated significantly with the CURB-65 pneumonia severity score calculated at the time of admission. Conclusions. Soluble-TREM-1 expression is upregulated in patients with both CAP and PTB, but does not differentiate these two conditions. Sputum concentrations of s-TREM-1 may predict the severity of disease in patients with CAP.