Four children were diagnosed with idiopathic pulmonary hemosiderosis (IPH), over a period of 4 years. Retrospectively, antineurtrophil cytoplasmic antibodies (ANCA) were studied by indirect immunofluorescence (IIF) and ELISA in 18 sera from these patients, stored at -20 degrees C. ANCA-positive sera, from 1/20 to 1/1, 200 dilution, were found in 3/4 of the patients, by IIF. The patient with the highest titre of ANCA died 3 months later during an acute crisis, the other two patients need a minimal dose of steroids. In one case only, a patient who is still without treatment, had no ANCA. The antibodies anti-myeloperoxidase and anti-proteinase-3 were negative or at border line levels. Rheumatoid factor, antinuclear (Hep-2), anti-endomysial, anti-reticulin and antibasement membrane antibodies were negative in all sera. The surviving patients were followed-up for more than 10 years with no systemic or renal disease appearances. The presence of serum ANCA may help to classify children with pulmonary haemorrhage and may have a prognostic value.