Much of the earlier apprehension concerning the toxic effects of viosterol (irradiated ergosterol) has been dispelled by more recent clinical observations. The early reports of A. F. Hess, Lewis and Rivkin,1Pfannenstiel,2Kreitmair and Moll,3Bamberger and Spranger,4and numerous others concerning the toxicity of viosterol are too well known to be reviewed at this time. It is questionable how reliable the early clinical observations and animal experiments may be considered, as most of the preparations employed before 1929 were standardized gravimetrically and not biologically, and accordingly could not have been constant in potency. More recent reports of A. F. Hess,1J. H. Hess, Poncher, Dale and Klein,5Grayzel, Shear and Kramer,6and others offer sufficient evidence that viosterol may be given over long periods in doses many times as large as those usually recommended without any danger Two brothers of Armenian parentage,