A silver-resistant mutant of Klebsiella pneumoniae B-5 was produced by passaging in nutrient broth containing graded concentrations of silver nitrate up to 150 ppm. The development of silver resistance in the strain resulted in rough colonies, decrease in cell size, carbohydrate content and change in klebocin pattern. The virulence of the AgR strain as checked by the burn wound model decreased as the mutant could not establish itself in the skin and spleen of the animals and the organism was cleared more efficiently by human lymphocytes than the parent AgS strain.