Two new quinoline compounds, enoxacin (600 mg) and norfloxacin (400 mg) were administered consecutively to six healthy male volunteers. The levels of the two agents were measured in serum, urine and blister fluid. The mean peak serum level of enoxacin was 3.7 mg/l and attained at a mean time of 1.9 h after administration; the mean peak serum level of norfloxacin was 1.45 mg/l at a mean time of 1.5 h. The mean serum half-lives were 6.2 h for enoxacin and 3.25 h for norfloxacin. Both agents penetrated blister fluid well and reached maximum levels of 2.9 mg/l (for enoxacin) and 1.0 mg/l (for norfloxacin). The 24 h urinary recovery of enoxacin of 61% was about twice that of norfloxacin. No adverse effects of either agent were observed. The data suggest that enoxacin might be used as a once daily dose for the treatment of urinary tract infections, but twice daily for the treatment of susceptible pathogens causing systemic (as against urinary) infections.