Twenty-five patients with severe urinary tract infections were treated with 3 mg of tobramycin/kg per day (given in two doses). Susceptible organisms were Escherichia coli, Proteus, Klebsiella, Pseudomonas, Streptococcus, and enterococcus. Clincal conditions in which treatment produced excellent bacteriological results included a wide range of urological disorders; the most common were pyelonephritis, cystitis, and epididymo-orchitis, Three patients had septicemia, and 12 had an infection that was the result of urinary tract obstruction requiring surgery.