Urinary tract infections in the elderly are severe and intractable, often justifying the use of aminoglycosides. We studied the effects of dibekacin in 28 patients, with no vesical catheter, whose average age was 78 +/- 6.1 years. The drug was given for ten days, in an average dose of 2.1 mg/kg/day divided into two injections. Serum concentration was measured after one hour on day 1 and after eight hours on days 1 and 10. Causative pathogens, all susceptible to dibekacin, were: 18 E. coli, 3 Proteus mirabilis, 3 Klebsiella, 1 Enterobacter cloacae, 1 Citrobacter and 2 Staphylococci. MIC and MBC of dibekacin were determined for each microorganism. Dibekacin was discontinued in four cases on day three because of persistent bacteriuria. Ten days after treatment end, 19 patients were cured, 4 had a relapse and 1 was reinfected. Average serum concentration of dibekacin, measured after eight hours, increased from 0.77 +/- 0.48 micrograms/ml on day 1 to 1.78 +/- 1.22 microgram/ml on day 10 (t = 4.42; p less than 0.0005), while, over the same period, there was no significant change in serum creatinine.