its presence and may presumably remain silent for prolonged periods. Occasionally, the clinical course of Hashimoto's disease may be punctuated by episodes simulating acute or subacute granulomatous thyroiditis, presumably of viral etiology. Thus, it is possible that our patient's thyroid may have been the site of clinically silent Hashimoto's disease, with the insidious development of fibrous changes over a prolonged period. The acute onset of symptoms may have represented an intercurrent infectious or inflammatory episode. Even so, the association of extreme pain and tenderness with the appearance of myxedema 6 weeks after onset remains difficult to explain.It is hoped that future immunologie studies in patients with invasive fibrous thyroiditis may further elucidate the significance of such mechanisms in thyroid disorders, and the etiology of this entity in particular. Summary An unusual case of invasive fibrous thyroiditis (Riedel's struma) occurred in a 24-year-old woman.The onset of symptoms was acute with fever, malaise, and marked pain and tenderness in the thyroid. Six weeks later the patient was myxedematous with a very large, hard, tender goiter. Tests for thyroglobulin and complement fixing antibodies in her serum were positive approximately 45 and 62 months after the onset of symptoms. The significance of these findings can be variously interpreted but not definitely explained. 36th & Spruce Sts. (4) (Dr. Rose). We are indebted to Dr. A. M. Bongiovanni for performing the original thyroglobulin erythrocyte agglutination test, and to Dr. Deborah Doniach for subsequent immunologie tests and comments. References 1. Riedel, B. M. K. L.: Die chronische, zur Bildung eisenharter Tumoren f\l=u"\hrendeEntz\l=u"\ndungder Schilddr\l=u"\se,