Rheumatoid pleuritis characteristically occurs in middle-aged male rheumatoid patients and may antedate the arthritis. The pleural fluid is an exudate, frequently turbid, and may be milky. The glucose content of the fluid is less than 30 mg/100 ml in 70% to 80% of effusions. A low glucose level in pleural fluid that is nonpurulent, negative for bacteria on smear and culture, and negative for malignant cells on cytologic examination almost invariably indicates that the effusion is due to rheumatoid pleuritis unless pleural biopsy reveals tuberculosis.