Lung function was prospectively studied in a group of non-selected systemic lupus erythematosus (SLE) female patients who consecutively came to our Lung Function Laboratory. There was no previous history of smoking in any patient nor there was clinical and/or radiographic evidence of lung affectation prior to the diagnosis of SLE. Some respiratory lung function abnormalities were observed in 17 patients (65%). The most frequent functional anomaly was the alteration in carbon monoxide transfer (DLCO), which was present in 10 cases (38%). On the other hand, a restrictive ventilatory failure was observed in 8 patients (31%) and a obstructive ventilatory failure in 6 other (23%). Out of these, 3 patients (12% of the total number of cases) presented bronchial hyperreactivity, which could also be confirmed in a patient presenting a mixed ventilatory failure. Isolated air entrapment could be observed in 2 patients, which could indicate disfunction of small airways in these cases. There was no correlation between functional respiratory failure and clinical activity of SLE, duration of the disease, other organ involvement, treatment and/or serum antibodies. Given that a great number of these functional lung anomalies (42%) exist in the absence of any clinical and radiological anomalies and that an important subgroup of patients are responsive to bronchodilators, we consider that the systemic evaluation of lung function must be obliged in the clinical treatment of SLE patients.