The influence of pretreatment with a three day course of ciprofloxacin (500 mg twice daily) on a single oral dose of ethanol (30 g) was investigated in 12 healthy male volunteers in a double blind placebo controlled study. Pretreatment with ciprofloxacin was shown to have no significant effect on ethanol AUC (736 mg.l-1 h placebo; 734 mg.l-1 h ciprofloxacin), Cmax (466 mg.l-1 placebo; 483 mg.l-1 ciprofloxacin) tmax (0.6 h placebo; 0.5 h ciprofloxacin) or the elimination rate (134 mg.l-1 h-1 placebo; 133 mg.l-1 h-1 ciprofloxacin). The effect of ciprofloxacin on ethanol pharmacodynamics was measured by the use of psychomotor tests, such as the critical flicker fusion threshold, choice reaction time, pursuit rotor, tapping rate, digit symbol substitution and digit span. Subjective feelings of concentration, vigilance and relaxation were also measured using visual analogue scales. Pretreatment with ciprofloxacin was found to have no significant effect on any of these tests, compared to placebo.