High performance liquid chromatography procedures have been developed for the assay of ondansetron-selected medications in 0.9% sodium chloride injection USP. The separation and quantitation of each mixture were performed on either an underivatized silica column or a bonded phase column at ambient temperature using either a methanol or acetonitrile-phosphate buffer mobile phase in the 4–5.4 pH ranges with detection set at 254, 233 or 210 nm. The separations were usually achieved within 20 min. Linearity, limit of detection, retention and tailing factors, resolution, accuracy and precision were calculated for each mixture.