Six patients with lymphomatoid granulomatosis were studied. Two patients had eye involvement, a rare manifestation of this disease. Both had complete disappearance of disease in this area after radiation therapy. One patient presented with an autoimmune hemolytic anemia, which remitted completely with chemotherapy. The use of corticosteroids or chemotherapy was effective in bringing about a decrease in pulmonary infiltrates in all six patients, although the duration of response was limited. One patient did have a prolonged period of clinical remission, and died of an unrelated cause. Evidence of profound immunologic abnormalities was found in these patients by a variety of tests. The extensive immunologic dysfunction present in patients with lymphomatoid granulomatosis has not previously been described. Most strikingly, patients with lymphomatoid granulomatosis have a severe impairment in T-lymphocyte function, confirmed by their inability to react to common skin test antigens or dinitrochlorobenzene, decreased in vitro lymphocyte responsiveness to mitogens and antigens and changes in T-cell subset populations. This may account for the frequent development of malignant lymphomas in patients with this condition.