Bronchial provocation tests (histamine and acetylcholine) were performed in 40 subjects (30 of them with type 1 diabetes, and 10 healthy volunteers) without any history of respiratory disease, not smoking and not taking any bronchodilating drugs. Bronchial reactivity was assessed using PC20 estimated spirographically by measuring FEV1. The patients were classified into three groups according to the duration of the disease: group I (0-7 yrs), group II (8-15), and group III (> 15). In all the three groups diabetes was at a similar degree of compensation, as evaluated by the mean circadian glycaemia, serum fructosamine and the Schlichtkrull Mw index. Bronchial reactivity to acetylcholine and histamine decreased with diabetes duration. Reaction to acetylcholine was statistically lower after 7 years of diabetes. An autonomic neuropathy was detected within the respiratory system, parallel to tachycardia at rest, alteration of the Valsalva test and orthostatic hypotension.