Beryllium exposure in the workplace can result in chronic beryllium disease, a granulomatous lung disorder characterized by CD4(+) T cell alveolitis and progressive lung fibrosis. A large number of the CD4(+) T cells recruited to the lung in chronic beryllium disease recognize beryllium in an Ag-specific manner and express Th1-type cytokines following T cell activation. Beryllium-responsive CD4(+) T cells in the bronchoalveolar lavage (BAL) express an effector memory T cell phenotype and recognize beryllium in a CD28-independent manner. In this study, we show that the majority of beryllium-responsive CD4(+) T cells in BAL have lost CD27 expression, whereas a subset of beryllium-responsive cells in blood retains expression of this costimulatory molecule. In addition, loss of CD27 on BAL CD4(+) T cells inversely correlates with markers of lung inflammation. A small population of BAL CD4(+) T cells retains CD27 expression, and these CD4(+)CD27(+) T cells contain the FoxP3-expressing, naturally occurring regulatory T (T(reg)) cell subset. Coexpression of CD27 and CD25 identifies the majority of FoxP3-expressing T(reg) cells in blood and BAL, and these cells express potent suppressor function. Taken together, these findings suggest that CD27 is differentially expressed between effector T cells from the inflamed lung and can be used in conjunction with CD25 to isolate T(reg) cells and assess their functional capacity in an ongoing adaptive immune response in a target organ.