Abnormalities of pulmonary function tests have been described in type 1 (insulin-dependent) diabetes mellitus (IDDM). To better characterise such abnormalities and to verify whether these latter are associated with the presence of diabetic microvascular disease we compared 23 non-smoking patients who had IDDM with 24 non-smoking healthy control subjects strictly matched for sex, age, and body mass index. Compared with controls, diabetic patients had a reduced forced vital capacity (FVC) (87.5 +/- 13.1% vs. 96.4 +/- 13.6% of the predicted; P = 0.03) and forced expiratory volume in 1 s (FEV1) (90.5 +/- 17.7% vs. 101.2 +/- 13.2% of the predicted; P = 0.02). While within the group of patients the presence of retinopathy and autonomic neuropathy were not associated with modifications of pulmonary function tests, those with altered urinary albumin excretion rate (AER > or = 20 micrograms/min; range 21-589) (n = 7) had a significantly lower pulmonary diffusion capacity (DLCO) than the 16 normoalbuminuric subjects (62.6 +/- 7.2% vs. 88.7 +/- 20.1% of the predicted; P = 0.01). Moreover, in the group of patients, DLCO was inversely related with AER (r = -0.43; P = 0.04). In conclusion, IDDM is characterised by reduced FVC and FEV1, while a significant decrease in DLCO may be considered as selectively associated with renal disease.