Providimcia stuartii has been widely reported as a cause of nosocomial infection, particularly urinary tract infection, but the epidemiology of these infections is poorly understood (Penner et al., 1979; McHale et al., 1981). The organism has been isolated from equipment that has been in contact with infected urine (Epidemiological Research Laboratory of the Public Health Laboratory Services, 1977) and external urine drainage devices (Frierer & Ekstrom, 1981). Asymptomatic urinary and faecal colonization of patients also constitutes another reservoir of infection within hospitals (Hawkey et al., 1982). Prov. stuartii is typically resistant to a wide range of antibiotics including gentamicin (McHale, Keane and Dougan, 1981). Since small numbers of bacteria present in the gastrointestinal tracts of colonized patients may be a source of cross-infection, particularly when their growth is encouraged by antibiotic treatment, a sensitive technique is required for their detection in faecal samples. The technique of pre-enrichment followed by the use of selective media has been described for the isolation of salmonellae from chicken giblets (Harvey & Price, 1981), but it has not been used previously, to our knowledge, for the detection of antibiotic-resistant bacteria in hospital infection. We describe here a method in which small inocula of gentamicin-resistant Prov. stuartii in faeces were pre-enriched in heart infusion broth. Selection for gentamicin-resistant organisms was then made on solid gentamicin-containing medium. The behaviour of Prov. stuartii in this system was compared with that of other gentamicin-resistant bacteria, Klebsiella aerogenes and Serratia marcescens.