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Plant hormones are important molecules which at low concentration can regulate various postharvest physiological processes. Mass spectrometry has become a powerful technique for the quantitation of multiple classes of plant hormones because of its high sensitivity and selectivity. We have developed a new ultra high pressure liquid chromatography-full scan high definition accurate mass spectrometry method (UHPLC-Q-TOF MS) for simultaneous determination of nine key plant hormones (abscisic acid (ABA) and four ABA metabolites, cytokinins (zeatin, zeatin riboside) and gibberellins (GA1, GA4). The compounds were extracted with methanol-water-formic acid, purified by Sep-Pack plus C18 and Oasis MCX cartridges, and separated and quantified by UPLC Q-TOF MS using an electrospray ionization source in both negative and positive modes. The method was validated by determining the linearity (R-2 >= 0.999) over the concentration range of 5-150 ng ml(-1) for most compounds. The limits of detection (LODs) of the technique, for example, ranged between 0.25 and 1.41 ng ml(-1) for abscisic acid (ABA) and 7'hydroxy abscisic acid (7'OH-ABA) respectively, with limits of quantitation (LOQs) between 0.87 and 4.70 ng ml(-1), respectively. Precision of the method was obtained with intra-and inter-day relative standards deviations (<= 4.2%) and accuracies for compounds typically ranging between 92-112. Recoveries were evaluated on spiked potato samples using SPE C18 and Oasis MCX cartridges. In addition, we evaluated the mass accuracy for most compounds (<2 ppm) achieving similar results for those obtained with FT-ICR and Orbitrap instruments.