A 33-year old housewife who developed BOOP in a flare-up stage of SLE was reported. She had been treated for Hashimoto's thyroidtis since the age of 18. When the patient was 21 years old, she noticed polyarthritis and subcutaneous nodules. She had a high titer of rheumatoid factor and a diagnosis of rheumatoid arthritis was made. At the age of 23, ulnar drift was noted despite the lack of subjective and objective signs of active articular inflammation. At the age of 25, she developed dry eyes and dry mouth, and at the age of 27, photosensitivity was experienced. At the age of 28, she was first admitted to our department and diagnosis of Sjögren's syndrome and SLE was made. Since then, she had been treated by corticosteroid and remained in a stable condition. In January 1991, she developed facial erythema, dry cough and edema of the lower extremities. Laboratory findings included profuse proteinuria, hypoalbuminemia, hyperlipidemia, elevated anti-DNA titer, depressed serum complements. Chest X-ray films showed a presence of patchy non-segmental infiltrates in both lung fields. TBLB specimen showed the characteristic findings of BOOP described by Epler at al. She had marked ulnar deviation at the MCP joints bilaterally and X-ray findings were consistent with Jaccoud's arthropathy. The pulmonary lesions and nephrotic syndrome responded to the combined therapy of prednisolone and immunosupressants. An occurrence of BOOP associated with flare of SLE indicates that immunological mechanisms might be involved for development of BOOP. Indeed, review of the literature shows that substantial numbers of patients with BOOP had clinical and serological overlapping findings with autoimmune diseases.(ABSTRACT TRUNCATED AT 250 WORDS)