Experiment s were conducted to see if Erwinia amylovora (Burrill) Winslow et al. overwinters inside living host tissue in Utah. Bacteria, collected from apple, pear, mountain ash, chokecherry and Pyracantha, were used in the experiment. Isolates taken from buds and inner bark plated on nutrient yeast dextrose agar, we re tested by serological and bacteriophage techniques. Those showing positive tests were then inoculated into Bartlett pear seedlings to test virulence. Both virulent and avirulent isolates were isolated from each species of plant in the experiment. Pathogenic bacteria were isolated from diseased tissue near cankers, as well as from apparently healthy inner bark as far as six inches below the cankers. Pathogenic bacteria were also isolated from healthy appearing buds in the vicinity of cankers. Nearly 15 percent of isolates from hosts other than apple and pear were pathogenic to Bartlett pear seedlings. A good deal of variation existed among the bacterial isolates. Antisera developed from four isolates of Erwinia amylovora proved to be a good means of identification for the pathogen.