DIFFUSE interstitial pulmonary fibrosis of the type originally described by Hamman and Rich1remains a most perplexing process, which, despite its striking histological appearance, may well represent a reaction peculiar not to one but to several inciting factors. Obscure in etiology and supposedly rare in occurrence, this syndrome is nevertheless so conspicuous by the extent of pulmonary involvement, so vicious in its relentless, usually unresponsive course, and so often fatal in its outcome that it is not surprising to note the current display of interest in the subject, as a growing number of case reports and a recent editorial inThe Journal of the American Medical Associationattest.2 Contrary to an erroneous concept being perpetuated in the literature, the original paper by Hamman and Rich appeared not in 1944 but in 1935.1Fully nine years elapsed before they published what has come to be regarded as the