A 56-year-old man suffered from prolonged fever, sore throat and cough, followed by pleural effusion and reversible progressive ascending muscle weakness. The condition fulfilled the diagnostic criteria of Guillain-Barré syndrome. Tuberculosis was initially suspected because of lymphocyte predominance and high adenosine deaminase activity in the pleural fluid. Later, an agglutination titer of 10,240 to Francisella tularensis antigen was found and an infected hare exposure could be identified. Thus, the activity of adenosine deaminase may be high also in tularemia pleuritis.