1. -Kveim's test (KT) was carried out on 104 patients for whom the diagnostic of sarcoidosis was suspectid. The positive results of KT correlate with other clinical, radiological and histological criteria. 2. - Two patients with idiopathic agammaglobulinemia (AGG) had positive KT. In two other cases of AGG, KT was negative. Two hypothesis are discussed: a) the association of AGG and infraclinical sarcoidosis favorized by the immunological deficit; b) false positive reactions, which raise the question of the specificity of KT. 3. - Lymphocyte transformation test in the presence of Kveim's antigen (LLT-K) was carried out simultaneously with KT 46 times. Among 30 positive KT only 20 LLT-K were positive. Among 16 negative KT 3LLT-K were positive. LLT-K was the only test carried out on 47 subjects. It was negative among 19 healthy control subjects, 19 allergic subjects and 7 patients suspected of sarcoidosis. LTT-K was positive among 3 patients suspected of sarcoidosis and 1 patient with Hodgkin's disease. 4.- LLT-K like other in vitro tests, presents some advantages over the in vivo tests, in particular the rapidity of response. We found that LTT-K was less often positive when compared with KT. The question of specificity is also raised for LTT-K.