In this issue of the Journal, Luft, Bunker, and Enthoven discuss some intriguing data obtained from the Commission on Professional and Hospital Activities. For certain operations, such as open-heart surgery, mortality tends to vary inversely with the number of such procedures performed at each hospital. For other operations, such as cholecystectomy without incision of the common duct, operative mortality is not related to the frequency of those procedures. It is a bit surprising that the mortality rate for some operations is the same at hospitals where very few or a great many such procedures are performed. The relatively low . . .