The topical use of nicotinic acid and its esters has been studied for some time, especially in the field of rheumatology.* When the tetrahydrofurfuryl ester of nicotinic acid was used as a rubifacient, it was noted that in patients with true rheumatoid arthritis, tetrahydrofurfuryl ester showed no local erythema on application to the skin. This observation led to studies as to whether these findings could be used as a diagnostic test for the presence of or as an indication as to the activity of a rheumatic infection. The technique of testing consists in the application of approximately 1 gm. of the 5% ointment to an area on the flexor surface of the forearm, using an arbitrary 35 revolutions. A positive test shows an area of erythema and whealing, erythema alone or whealing alone (within 25 to 30 minutes). In contrast, patients with active rheumatic fever showed no reaction