An effective treatment for the advanced stages of chronic obstructive pulmonary disease (COPD) has not been established yet. We report our recent experience of one patient with pulmonary emphysema treated by dietary supplementation of n-3 fatty acid for two months. He presented improvements in clinical symptoms and pulmonary function, and suppression of leukotriene B(4) generation by peripheral leukocytes. We consequently suppose that dietary treatment with n-3 fatty acids (perilla seed oil) may offer benefits for the treatment of pulmonary emphysema by competitively inhiabiting the conversion of arachidonicacid to leukotrienes and prostanoids.