The aim of this study was to determine the value of the destination of T-lymphocyte subpopulations in bronchoalveolar lavage (BAL) fluid for the assessment of disease activity in pulmonary sarcoidosis in comparison with other tests of activity, i.e., lung function tests, angiotensin-converting enzyme (ACE), and gallium lung scan. According to clinical and roentgenographic data, 20 patients with biopsy-proven sarcoidosis were classified as having either active (nine patients) or inactive (11 patients) disease. Helper and suppressor T-lymphocyte subsets in BAL were identified by the peroxidase-antiperoxidase method performed on glass slides using murine monoclonal antibodies (OKT 3 for pan T-, OKT 4 for helper, and OKT 8 for suppressor T-lymphocytes). Patients with active sarcoidosis had significantly higher proportions of lung helper cells (90±5% of T-lymphocytes) than did patients with inactive sarcoidosis (65±11%) or control patients (63±7%),P<0.001. the="" proportion="" of="" lung="" helper="" cells="" correlated="" significantly="" with="" vital="" capacity="">r=–0.72,P<0.001), with="" total="" lung="" capacity="">r=–0.60,P<0.01), with="">₂ at rest (r=–0.46,P<0.05) and="" during="" exercise="">r=–0.54,P<0.05), and="" with="" co-diffusing="" capacity/1="" lung="" volume="">r=–0.53,P<0.05). there="" was,="" however,="" no="" correlation="" between="" lung="" lymphocyte="" subsets="" and="" serum="" ace="" or="" gallium="" lung="" scan,="" nor="" between="" ace="" and="" gallium="" scan.="" although="" ace="" and="" gallium="" uptake="" were="" higher="" in="" active="" sarcoidosis="" than="" in="" inactive="" disease,="" considerable="" overlap="" existed="" between="" groups,="" and="" the="" difference="" was="" not="" significant.="" thus,="" the="" proportion="" of="" helper="" cells="" in="" bal="" fluid="" appears="" to="" be="" a="" most="" useful="" parameter="" to="" assess="" activity="" of="" pulmonary="">