The clinical, pathologic, and immunopathologic findings of 14 patients with the toxic oil syndrome are presented. The toxic oil syndrome occurred in Madrid, Spain, as a consequence of ingestion of an industrial oil sold as olive oil. The syndrome occurred in two phases. In the acute phase patients developed an interstitial pneumonitis, fever, and exanthem, and some died of respiratory insufficiency. Of those who survived, some developed a chronic phase with a neuromyopathic and scleroderma-like illness that had many features of a collagen vascular disease. Histologic examination of lung in the acute phase showed an endovasculitis and features of adult respiratory distress syndrome. In the chronic phase the skin showed various degrees of sclerodermoid changes and vessel injury. Immunofluorescence with antiprocollagen and antifibronectin antibodies revealed abundant perivascular fluorescence suggestive of vascular injury. Electron microscopy corroborated this by the presence of endothelial swelling and basal lamina reduplication. Similar findings have been described in systemic sclerosis, and this provides an important model for study of connective tissue disease, including scleroderma.