A 10 yr old male with hypoxaemia, progressive infiltration on the chest radiograph and biopsy-proven desquamative interstitial pneumonia was treated with daily oral prednisolone for 6 months. Intravenous methylprednisolone pulses were concomitantly administered in doses averaging 10 mg x kg body weight(-1) on three consecutive days every 4-6 weeks. After 6 months improvement could be noted and oral steroids were stopped, while pulse therapy continued. Three months later, when seven pulses had been administered, a relapse occurred and the clinical status deteriorated. Instead of reinstating daily systemic steroids, the dose of methylprednisolone pulses was increased to 20 mg x kg body weight(-1) i.v. given on three consecutive days and repeat pulses every 4 weeks. This was followed by continuous improvement. After 24 months corticosteroid pulses were terminated. Normal lung function, serum lactate dehydrogenase, blood gases upon exertion and regular development was achieved. During the course of treatment, the child has grown 10 cm. It is concluded that the effect of corticosteroid pulse therapy on interstitial lung disease in childhood is dose-dependent and that the dose can be adjusted to the effect observed.