Sparfloxacin (SPFX) is a new quinolone compound with a long half-life of 16 hours and a potent antibacterial activity (MIC90: < or = 0.025 micrograms/ml against Escherichia coli), suggesting that the agent can be effectively used in single-dose therapy for acute uncomplicated cystitis in female patients. To find the optimum dose, the present dose-finding study was conducted. A dose of either 100 mg or 200 mg of SPFX was selected by the double-blind method, and was administered only once (single dose therapy). The clinical efficacy was judged on day 3, 7 and 14 after administration. On day 3, of the 49 pts. in the 100 mg-group, the efficacy rate was 95.9% (excellent rate: 79.6%), and of the 42 pts. in the 200 mg-group, it was 100% (excellent rate: 88.1%). On day 7, of 38 pts. in the 100 mg-group, it was 94.7% (excellent rate: 78.9%), and of 28 pts. in the 200 mg-group, it was 100% (excellent rate: 92.9%). On day 14, of 27 pts. in the 100 mg-group, it was 92.6% (excellent rate: 66.7%), and of 26 in the 200 mg-group, it was 96.2% (excellent rate: 84.6%). Recurrence was observed in 4.8% (1/21) in the 200 mg-group. Therefore, there was no significant difference in the efficacy rate between the two groups, but the rate of excellent responses was higher in the 200 mg-group. Otherwise, the efficacy was estimated to be insufficient in 3 pts. and recurrent in 1 pt. they were examined the findings of detailed urological intractableness. Among 2 pts. in whom the external genitalia and urethra were closely examined, a urethral caruncle was noted in 1 pt. The results of our study indicate that 200 mg of SPFX is recommended as a single dose therapy for acute uncomplicated cystitis in females.