A patient employed in a plant where blue cheese was manufactured developed hypersensitivity pneumonitis to Pencillium roqueforti. Symptoms of cough, dyspnea, and malaise, and findings of bibasilar crackles, reduced lung volumes, hypoxemia, and bilateral infiltrates on chest roentgenogram, resolved after she left the workplace. Bronchoalveolar lavage revealed a high percentage of lymphocytes. Antibody to P. roqueforti was demonstrated in serum and lavage fluid. To our knowledge this case represents a new occurrence of hypersensitivity lung disease in the cheese manufacturing industry in the United States.