A great deal of interest has been aroused by the recent reports on the favorable action of quinidin in auricular fibrillation. Since Frey's1 first publication in 1918, the results from the treatment of over one hundred cases have appeared, nearly half of which have been reported by Frey.2 The literature is given in the recent article by Levy,3 who also reports the results on four cases. The purpose of this report is to record the experience in the use of this drug in two cases selected from a number under observation in this clinic. The first of these cases is reported to bring out a point which in our opinion has not been emphasized sufficiently, namely, the danger in the use of this drug in certain cases. The other case illustrates the strikingly favorable action of quinidin in the rather rare condition in which auricular fibrillation is uncomplicated by advanced