One of the purposes of typing Pseudomonas aeruginosa is to identify strains within the species. Hospital infections committees are charged with surveillance of the spread of P. aeruginosa and the infections it causes. The importance of sinks in hospital epidemiology of P. aeruginosa is discounted since patient-to-patient infection is considered more common. For anyone contemplating bacteriophage typing, a decision must be made whether to isolate phages from P. aeruginosa strains and from sewage in order to derive a typing set or to request an existing set or sets from other laboratories. Bacteriophage patterns of a single P. aeruginosa strain are subject to considerable variation. Antibiogram differences would seem to have value in strain tracing of P. aeruginosa where there are outstanding departures from the normal values, particularly extreme resistance to antibiotics that are normally active against the organism. The amount of slime produced by P. aeruginosa strains influences attachment of phage or pyocin.