Chronic cor pulmonale is more prevalent in northern India than in the south. It is equally common in men and in women and accounts for 20% of all admissions for heart disorder in Delhi. In a study of 766 patients (239 men and 527 women) carried out over a 15-year period there were some striking sex differences. Some 75% of men and 10% of women smoked. The women came from the poorest class and all of them cooked from an early age over smoky and primitive fireplaces in ill-ventilated huts, while only 7% of the men cooked their own food. Chronic bronchitis and bronchiectasis were the commonest associated lung disorders in both sexes. The women developed heart failure 10-15 years earlier and showed more severe congestive failure with larger hearts and greater derangement of pulmonary function. It is concluded that the cause of chronic cor pulmonale in women in Delhi was damage to the lungs from exposure to smoky cooking fuels from girlhood onwards, followed by repeated chest infections.