Sporadic infections with Acinetobacter spp., punctuated with prolonged outbreaks of infection involving larger numbers of patients and a particular epidemic strain of Acinetobacter baumannii, have occurred in the adult intensive care unit (ICU) of Nottingham University Hospital since 1985. The aim of this study was to screen patients admitted to the ICU for three or more days during a non-outbreak period in 1994-1995 and to use DNA fingerprinting techniques to compare any isolates of Acinetobacter spp. with isolates obtained from the same ICU during the previous ten years. In the present study, almost 20% of the ICU patients screened during 1994-1995 became colonized with Acinetobacter spp. The commonest species isolated from patients was Acinetobacter baumannii; five different strains were identified by random amplified polymorphic DNA fingerprinting, including the epidemic strain responsible for outbreaks of infection in 1985-1986 and 1992-1993. Environmental sampling yielded Acinetobacter spp. from one or more samples on four occasions; Acinetobacter radioresistens was the commonest species isolated, and Acinetobacter baumannii (not the epidemic strain) was isolated on only one occasion from the environment. The long-term persistence of a potentially epidemic strain in the ICU, even during a non-outbreak period, indicates a need for continued vigilance. Consequently, periodic patient and environmental surveillance, combined with typing of isolates, is recommended for ICUs where significant outbreaks of Acinetobacter infection have occurred in the past.