Diabetes mellitus is known to be associated with impaired perception of sensory input from organs such as the heart. To determine whether diabetics have a diminished ability to perceive respiratory sensations, we compared the abilities of patients with insulin-dependent diabetes (n = 17) and nondiabetic controls (n = 13) to detect inspiratory-resistive loads. The subjects were evaluated as they breathed through a tube-manifold apparatus with resistance that was varied randomly. They indicated whenever they perceived increased resistance to inspiration. The threshold for detecting added inspiratory resistance was expressed as a fraction of the background resistance of the subject plus that of the apparatus. This fraction, known as the Weber fraction, was 0.53 +/- 0.19 (mean +/- SD) in diabetics with neuropathy, 0.38 +/- 0.24 in diabetics without neuropathy, and 0.29 +/- 0.15 in nondiabetic controls. The differences in the mean value of the Weber fraction among the three groups were significantly different from zero (F = 4.57, P less than 0.025). There was not a significant correlation between the Weber fraction and age, degree of autonomic dysfunction, pulmonary function, cigarette smoking, or degree of diabetic control. The Weber fraction correlated with the duration of diabetes (r = 0.57, P less than 0.02). We conclude that patients with insulin-dependent diabetes may have an impaired ability to perceive inspiratory-resistive loads. This increased threshold for the perception of respiratory sensations may lead to delayed recognition of pulmonary disease in diabetics.