[en] To evaluate the possible relationships between the stage of Sarcoidosis and the amount of cells in the lung, we studied the lung radioactive concentrations of two molecules which are greatly extracted there. Twelve patients, in supine position, were injected with an intravenous bolus of Imipramine or Propranolol labelled by cyclotron-produced ¹¹C. By Positron Emission Tomography 15 sequential images (2 min each) of a single transverse chest section were obtained. Curves of tracer concentration per cm³ of lung and per mCi of injected dose were plotted versus time and fitted as a single exponential. Only washout decay-constants were significatively lower (p < 0.02) in 5 subjects with sarcoidosis pulmonary infiltration (0.35 +- 0.11 h^-1, M +- S.D.) than in 5 normal subjects (1.39 +- 0.52 h^-1) or the 2 without pulmonary infiltration (0.92 and 1.19 h^-1). These data suggest a change in regional blood flow conjugated with a qualitative modification of the lung pools of the two products