The present invention provides a method for treating Hemophilia A or B which comprises implanting in fluid communication with the bloodstream of a mammal in need of such treatment a permeable membrane having one or more walls, a hollow chamber therewithin, a plurality of holes extending through the walls of the membrane and permitting fluid to enter and exit the chamber of the membrane, each of the holes being sized so that it is large enough to permit inactive Factor VII to enter the chamber of the membrane and activated Factor VIIa to exit the chamber of the membrane but small enough to prevent fibrinogen from entering the chamber of the membrane, a plurality of supports being disposed within the chamber, and an effective amount of a Factor VII activator or a source of the activator being bound to the supports, wherein inactive Factor VII in blood passing through the membrane becomes activated into Factor VIIa upon contact with the activator within the chamber. The present invention also provides a method for treating Hemophilia A or B extracorporeally. The present invention further provides methods for treating AIDS as well as permeable membranes for use in the methods above.