AbstractGross histomorphological alterations and biochemical changes, particularly in the lipid pattern of lung alveolar tissues, were oblerved in rats after intraperitoneal injection of capsaicin (the pungent principle of red hot pepper). Preliminary experiments showed that short‐term capsaicin treatment produced and inflammatory response with significant degenerative changes in the alveolar epithelial cells and increased cellularity of lung alveoli, as revealed by thickening of lung alveolar cells with occasional rupture of lung alveolar cellular integrity. The cytological changes were correlated with concomitant biochemical changes revealed by the decreased cholesterol and phospholipid content of lung alveolar tissues and infiltration of phospholipids towards the lumen of the alveoli which may be the cause of thickening of the alveoli cell lining of the lung tissues. On the other hand, long term capsaicin‐treated rat lungs showed a significant inhibition of capsaicin induced damage of lung tissues indicating a possible dual action of capsaicin on antiinflammatory respones in the pulmonary sys