The belief that cutaneous infection with pyogens plays an important part in the genesis of lesions of familial benign chronic pemphigus (FBCP) arose from a few chance observations and has been strengthened by experimental evidence. I propose beginning with an account of the steps by which this conclusion was reached and leaving a discussion of the previous literature to a later part of this paper. Report of Cases Case1.—A white woman, age 56, was first seen on July 27, 1951. Since the age of 17 recurrent vesicular and bullous lesions have affected the axillae and occasionally the sides of the neck. Attacks tended to occur in the late winter (i. e., July to September in South Africa) and to last for about six weeks. Intervals of freedom varied from a few months to several years. In the past, a few exposures to roentgen rays had always