Microbe Base is a national computerized database comprising in excess of 1.7 million patient records down-loaded from the laboratory computer systems of 61 participating UK laboratories over 10 years. This paper highlights the antimicrobial susceptibilities of organisms isolated from the urinary tract which comprise around 50% of all isolates in the database. These data may be used to determine trends in antimicrobial susceptibilities; to formulate local antibiotic policies; to compare local with national data and, overall, to assist clinicians in the rational choice of antibiotic therapy and to prevent misuse, or overuse, of antibiotics.