The effect of insulin-dependent diabetes mellitus on pulmonary function was studied in 22 diabetic nonsmokers (11 men) with a mean age of 40 yr (SE, 4 yr) and no history of cardiorespiratory disease. Exponential analysis of static pressure-volume data obtained during deflation of the lungs gave the exponent K, an index of pulmonary distensibility. In the diabetic subjects, mean values for total lung capacity, functional residual capacity, VC, and FEV1 were similar to predicted values. Diffusing capacity, K, and in K did not differ significantly from corresponding values in healthy subjects. The regression of in K on age was significant (R = 0.52; p less than 0.01) and similar to that obtained for 124 healthy subjects. The findings show that insulin-dependent diabetes mellitus does not affect pulmonary function. This study does not support the routine testing of lung function in otherwise well diabetic nonsmokers.