Spectinomycin hydrochloride 140 mg/kg/day and gentamicin 3 mg/kg/day were evaluated in the treatment of 50 hospitalized patients with urinary tract infections. Seven patients (28%) in the spectinomycin group had positive urine cultures after 72 hours of therapy due to initial resistance of the organism (5 isolates) or development of resistance to spectinomycin (2 isolates). Response to gentamicin therapy was uniformly satisfactory. Complications of spectinomycin therapy included pain and induration at the injection site (11 patients) and elevated serum creatinine values (2 patients). Ototoxicity was noted in three patients given gentamicin. Peak serum concentrations of spectinomycin (range 55-157 microgram/ml) and gentamicin (range 2.8--8.5 microgram/ml) showed marked interpatient variation. Spectinomycin appears to be of limited value in the treatment of urinary tract infections caused by gram-negative bacilli.