During a two year period from 1979–1981, gentamicin- and multiple-resistant strains of enterobacteria were isolated from 260 patients. All isolates showed a similar resistance pattern and consisted of Escherichia coli, Citrobacter, Enterobacter, Proteus, Providencia and Klebsiella spp. Klebsiella was the commonest isolate and the organism responsible for cross-infection. The 32 different capsular serotypes encountered in the present outbreak represent a far greater diversity of gentamicin-resistant klebsiellae than has been reported previously. Of these, however, capsular serotypes K39, K2, K68, K43 and K54 accounted for more than two-thirds of the typable strains. The majority of infections followed manipulation of the urinary-tract and were often associated with in-dwelling urinary catheters or were in immunosuppressed patients. The inanimate environment in close contact with patients was infrequently contaminated and then only with klebsiellae. The bed-pan macerators occasionally released an aerosol containing gentamicin-resistant klebsiellae. The majority (83 per cent) of sluice sinks were heavily contaminated with many different gentamicin-resistant enterobacteria including 22 different klebsiellar capsular serotypes.