Abstract
The ureases produced by a large number of strains of different Proteus species, some of which were known to have a special affinity for the urinary tract, were examined by polyacrylamide-gel electrophoresis. Each Proteus strain gave a pattern of urease isoenzymes that was characteristic and unique to its species although strains of P. Mirabilis and P. vulgaris gave isoenzyme patterns that were closely similar. There was some minor variation in the patterns of urease isoenzymes even between strains of the same species. This was most noticeable among P. rettgeri strains and to a lesser extent among P. vulgaris strains. No correlation was found between the types of ureases a strain produced and its pathogenicity for the urinary tract.