In their investigations into bronchospasm, Crofton, Douglas, Simpson, and Merchant (1963), and Douglas, Simpson, Merchant, Crompton, and Crofton (1966a and b) have found that a ratio of endomural bronchial pressure to oesophageal pressure in wheezy patients is frequently above unity. They suggested that this might be due to active bronchial muscle contraction on expiration. In a series of lungs we examined the evidence for an alternative theory of a radial traction effect which could explain their findings. The lung was placed in an airtight jar and inflated and deflated, the pressure excursion (J) inside the jar being recorded. Simultaneously, the endomural bronchial pressure excursion (B) was recorded by means of a specially designed probe. The ratio of these two excursions (B/J ratio) was calculated. A ratio of less than unity was consistently obtained, suggesting a simple pressure gradient in the lung. No evidence of a radial traction effect was found in the size of bronchi (4 mm.) measured, though of course such an effect could not be excluded in other sizes of bronchi or in bronchioles.