Henoch-Schönlein purpura (HSP) is a widespread necrotizing vasculitis affecting small vessels characterized by nonthrombocytopenic purpura. Pulmonary involvement is a rare fatal complication with diffuse alveolar haemorrhage. The objective of this study was to evaluate possible early lung function abnormalities and to establish any relationship with the clinical activity of the disease. Fifteen children with HSP and without clinical or radiological evidence of lung involvement underwent pulmonary function study at the onset of the disease. A sample of 28 subjects matched by age, height, and weight was chosen as a control group. After a mean of 21 months (range 12-43) lung function tests were repeated in 10 of the previously studied children. During the acute phase of the disease the transfer factor for carbon monoxide, measured by steady-state (TL,COss) and single-breath (TL,COsb) methods, was found to be significantly lower in children with HSP than control subjects. There was no significant relationship between pulmonary function tests with symptoms and signs at onset, nor was there any correlation between variables and serum immunoglobulin A (IgA) concentration. In all but two patients, clinical recovery was observed within 6 weeks from the onset of the disease. In one case relapses of purpuric skin lesions were observed during the first 3 months of follow-up. The second case had relapses of purpuric skin lesions and microscopical haematuria during the 12 months following the onset of the disease with characteristic IgA mesangial deposition on renal biopsy. Although the overall mean value of TL,COsb improved from baseline to the second investigation, in both patients the recurrences of clinical signs were associated with a slight impairment of TL,COsb at the second evaluation. These data suggest an early subclinical lung impairment in children with Henoch-Schönlein purpura during the active phase of the disease. The presence of isolated pulmonary function abnormalities was not associated with the subsequent development of lung disease.