Urinary 5-methoxytryptamine in patients with rheumatic fever.

No specific diagnostic test for rheumatic fever has been available to date (1). The tryptophannicotinic acid metabolic series was studied exhaustively in the present work. This investigation was based on a previous observation that the tetrahydrofurfuryl ester of nicotinic acid elicited a different response in the skin of patients suffering from active rheumatic fever than in the skin of nonrheumatic patients (2). The reaction was attributed to nicotinic acid, a member of the tryptophan metabolic series. The present report describes an abnormal product of tryptophan metabolism isolated from the urine of rheumatic subjects.