The size of bronchial mucous glands in 21 patients who presented with meconium ileus and died at less than three weeks of age were compared quantitatively with that of 28 control patients. There were no significant differences by most methods of comparison. However, pulmonary infection was seen in a higher percentage of cystic fibrosis patients. The absence of mucous gland hyperplasia at birth suggests that mucous obstruction of airways may not be primarily responsible for the increased susceptibility to respiratory tract infection in cystic fibrosis, but when present later in life may aggravate the infection.