120 women suffering from acute uncomplicated bacterial cystitis were treated in an open randomized study either with 1 X 400 mg enoxacin or 1 X 3 g amoxicillin per os. Analysis of midstream urine and bacteriological urine cultures were examined before, two and seven days as well as six weeks after therapy. Treatment with enoxacin resulted in 97.5% (second day), respectively 92.5% (seventh day) bacteriologically sterile urine cultures, whereas the rate of sterile urines following amoxicillin reached only 72.5% (second day), and 65% (seventh day), respectively. Side effects (gastrointestinal, allergic, cardiovascular) were noted in one case in the enoxacin group and in ten cases in the amoxicillin group. The highly active antibiotic derivatives of the 4-quinolone-group (e.g. enoxacin) administered as a single dose achieve high cure rates in carefully selected female patients with acute uncomplicated bacterial cystitis.