From 1980 to 1983, 69 patients (36 male) with end-stage renal disease underwent kidney transplantation (11 from cadaveric donors). Twenty-six out of 69 (17 male) with a mean age of 37 years (range 16-50 years) developed 69 UTI episodes. The standard immunosuppressive regimen consisted of prednisolone and azathioprine and, in selected cases, antilymphocyte globulin or cyclosporin A were given for a short period of time. Thirty-five episodes (50%) occurred within two months of the operation. The most commonly isolated bacteria were E. coli (28 cases), Ps. aeruginosa (16) and Proteus mirabilis (9). Kidney graft dysfunction, diabetes mellitus, urological complications and antirejection treatment were the main predisposal factors. Recurrence or reinfections were finally diagnosed in 19/26 patients (73%). Thirteen patients presented with asymptomatic bacteriuria (55% of episodes). Aminoglycosides, ureidopenicillins and third-generation cephalosporins were found to be very effective for treating severely ill, febrile patients. In addition, trimethoprim/sulphamethoxazole and mecillinam were useful for patients on long-term chemotherapy. There were no deaths or impairment of the renal graft function directly attributable to the urinary infection. In conclusion, UTIs are a very common cause of morbidity in kidney graft recipients, with the highest incidence in the early post-transplant period. Recurrences or reinfections occur often and asymptomatic bacteriuria is a common finding which needs not be treated aggressively in the absence of symptoms or obstructive uropathy. Patient and graft survival in the long term remain unaffected by the presence of the urinary infection.