Pneumocystis jirovecii has emerged as an important pulmonary pathogen. Historically associated with the immunocompromised, it is being increasingly observed in immunocompetent populations. (1→3)-ß-D-glucan (BG) is a major component of the cyst cell wall and plays an important role in the inflammatory response to the organism. Inflammatory synergy by co-stimulation with BG and Toll-like receptor ligands has been demonstrated in vitro and may be a factor in the pathophysiology of Pneumocystis pneumonia. Detection of highly elevated serum concentrations of BG in the serum of patients has been shown to be highly sensitive for the presence of pulmonary P. jirovecii.