Respiratory muscle strength and endurance were examined in 31 Type 1 diabetic patients and in age, sex, and weight matched control subjects. No significant difference in respiratory muscle strength was noted between the two groups. Maximal static inspiratory pressure was 92.3 +/- 33.9 (+/- SD) and 99.5 +/- 23.0% of the predicted values in the patient and control groups, respectively. Maximal static expiratory pressures were 75.1 +/- 14.3 and 77.4 +/- 14.0% of the predicted values in the patient and control groups, respectively. Respiratory muscle endurance was significantly lower in the diabetic patients 88.9 +/- 20.7 vs 103.9 +/- 15.8% predicted in the control group (p less than 0.01). Total lung capacity, vital capacity, and maximal voluntary ventilation were also significantly lower in the diabetic group and correlated with the duration of diabetes.