Last month's HEJ featured an article based on a presentation at a recent IHEEM seminar given by Dr Jimmy Walker, principal investigator, Decontamination, Biosafety Unit, Microbiology Services, at the Health Protection Agency, who provided valuable advice on detecting and dealing with Pseudomonas in hospital water supplies. Here Dr Walker, and HPA colleague, Peter Hoffman, consultant clinical scientist at the Agency's Laboratory of Healthcare-associated Infection, Microbiology Services, give a detailed overview of the key characteristics of Pseudomonas aeruginosa biofilms, and describe some of the most effective ways for controlling their spread in hospital water systems.