RESUMEN
101 cases of idiopathic interstitial lung disease diagnosed by lung biopsy, were reviewed according to clinical and X-ray appearance and especially to their response to steroid therapy. Four morphological inflammatory reactions are distinguished: (1) alveolitis; (2) onion-like mesenchymal proliferation; (3) sarcoid-like lesions, and (4) lymphofollicular reactions. Especially type 1 and/or type 2 show immediate response to steroid therapy. Only a few cases showed spontaneous improvement. Once a fibrosis exists, a 'restitutio ad integrum' cannot be expected any where. From this group of idiopathic interstitial lung diseases the conclusion seems to be justified that also other types of interstitial lung reactions should be treated with steroids to avoid it turning into lung fibrosis.