DESPITE appropriate systemic antibiotic therapy and conservative surgical measures, certain severe infections of the extremities frequently progress to threaten life, necessitating amputation. Regional perfusion, affording high concentrations of the appropriate antibiotic along with a high oxygen tension in the afflicted area, can obviate such radical therapy. Laboratory data in support of this thesis, and a successful clinical application of this approach, are reported. Experimental The dog was chosen for study because (1) it is well suited for regional perfusion of the hind limb, and (2) is reasonably susceptible to Clostridium welchii infection, as Altemeier has reported. 1 Five strains of lyophilized C welchii were obtained from the American Type Culture Collection (ATCC) in Washington, DC, and these, along with several strains cultured from clinical infections at Jackson Memorial Hospital, were subjected to virulence studies in the guinea pig and dog. ATCC No. 10543, source unknown, proved to be the