Ciprofloxacin is a broad-spectrum antibacterial drug, being used in a wide range of infections. A method to quantify the total (unbound + protein-bound) ciprofloxacin concentrations in human serum is presented based on rapid liquid-liquid extraction, followed by reversed-phase liquid chromatography and UV detection at 280 nm. The calibration range used was 2 to 10 mg/L. The mean accuracy and precision (CV%) were all within specifications: at 0.2 mg/L 81.2% (10.1%), assigned to be the lower limit of quantification (LLOQ), at 8 mg/L 103.6% (4.48%), at 14 mg/L 103.1% (3.98%). Metabolites and frequently used comedications showed minimal interference. Sample storage conditions suitable for routine determination of serum ciprofloxacin concentrations for daily therapeutic drug monitoring (gel-collection tubes and PVC tubes at 4 degrees C) and for intermittent batch-wise analyses for research purposes (PVC tubes at -18 degrees C) showed acceptable sample stability after storage for 48 hours (4 degrees C) and 6 months (-18 degrees C).