This article outlines a rapid simple and reliable method for diagnosing citrus yellow shoot (YS) it was named "direct fluorescence detection method" . Thin leaf section were prepared from fresh tissues of YS-lnfected and healthy citrus plants, when observed under a fluorescence microscope (Type, Olympus AH-FL-2), a yellow fluorescence was distinctly observed in the YS-infected phloem tissues and not in the phloem tissuses of healthy plants and of those infected with tristeza, exocortis, canker, scab, greasy spot, Mg and Za deficiency.