Static lung pressure-volume curves, lung volumes, spirometry, diffusing capacity for CO, and airway and total pulmonary resistance were determined in 11 young men with juvenile-onset diabetes mellitus who were not cigarette smokers. Twelve nonsmoking men of similar age without diabetes served as control subjects. Elastic recoil at low lung volumes was significantly less in the diabetics than in the control group. Total lung capacity was also decreased in the diabetics. There were no significant differences between the 2 groups in the other parameters of pulmonary function measured. It is postulated that the abnormalities in lung elastic behavior are manifestations of the widespread elastin and collagen abnormalities that have been demonstrated in diabetes and are, in some respects, similar to those that occur during normal aging. Loss of elastic recoil at low lung volumes may cause more significant decreases in flows and gas transport as the juvenile diabetics age.