OBJECTIVE. To investigate the distribution of hospital pathogens within general and critical care ward environments and to determine the most significant bacterial reservoirs within each ward type. DESIGN. Prospective 4-month microbiological survey. SETTING. The intensive care unit (ICU) and gastrointestinal (GI) surgical ward of a London teaching hospital. PATIENTS. Sampling was conducted in and around the bed space of 166 different patients (99 in the ICU and 67 in the GI ward). METHODS. Conventional agar contact methodology was used to sample 123 predetermined sites twice a week for 17 weeks. Sixty-one surfaces were located within the ICU, and 62 were located within the GI ward. Each surface was located within a theoretical zone of increasing distance from the patient. Aerobic colony counts were determined, and confirmatory testing was conducted on all presumptive pathogens. RESULTS. Regardless of ward type, surfaces located closest to the patient, specifically those associated with the bed (side rails, bed control, and call button), were the most heavily contaminated. Elsewhere, the type of surfaces contaminated differed with ward type. In the ICU, bacteria were most likely to be on surfaces that were regularly touched by healthcare workers (e.g., telephones and computer keyboards). In the GI ward, where the patients were mobile, the highest numbers of bacteria (including potential nosocomial pathogens) were on surfaces that were mainly touched by patients, particularly their toilet and shower facilities. CONCLUSIONS. In terms of cleaning, a hospital should not be considered a single entity. Different ward types should be treated as separate environments, and cleaning protocols should be adjusted accordingly.