During a 10-month period, from October 1984 to July 1985, a multi-resistant strain of Acinetobacter anitratus was isolated from 36 patients in three neurosurgical wards, one medical ward and the intensive care unit of a district general hospital, and from two patients in the intensive care unit of a hospital in another district. Fourteen patients developed significant infection including pneumonia (10), meningitis (2), septicaemia (2) and wound infection (4). The majority of cases (28) involved the respiratory tract of ventilated patients, although respiratory equipment was not implicated as a source of the infection. The epidemic strain was recovered from the skin, nose, mouth and rectum of colonized patients and from the hands of personnel. However, extensive air and environmental contamination in the vicinity of colonized patients was also demonstrated. This is the first outbreak of infection with Acinetobacter, of which we are aware, where airborne spread has been observed.