Sarcoidosis is a multisystem granulomatous disease of unknown origin. No single biological marker allows definitive diagnosis of sarcoidosis or may accurately predict the disease prognosis. However, some biological markers are helpful tools as diagnostic aids and disease activity markers. At the blood level, lymphopenia with CD4 depletion, elevated levels of serum-angiotensin converting enzyme, lyzozyme, beta 2 microglobulin and disturbed calcium metabolism resulting in hypercalcemia and hypercalciuria can help guide diagnosis. Lymphocytic alveolitis with a high CD4/CD8 ratio in bronchoalveolar lavage fluid is highly suggestive of the disease. A wide range of new biological markers are proposed but their pronostic significance is still controversial. In clinical practice, biological markers may help in monitoring treated patients with sarcoidisis.