Eight fluorescent dyes were tested for staining the spores or mycelia of six fungi and for their translocation into new growth when the preloaded spores or mycelia were incubated on agar coated coverslips. The dyes studied were Cellufluor, Nile red, fluorescein diacetate (FDA), carboxyfluorescein diacetate (CFDA), chloromethylfluorescein diacetate (CMFDA), aminochloromethyl coumarin (CMAC), and the carbocyanines DiIC18(3) and DiOC18(3). The fungi on which the dyes were tested includedBotrytis cinerea, Fusarium oxysporumf.sp.lycopersici, Idriella bolleyi, Pythium oligandrum, Sclerotium cepivorumandTrichoderma. harzianumMost of the fluorochromes gave good initial staining of mycelia or spores; however, FDA fluorescence faded rapidly during excitation, making it impractical for use. Also, the spores and mycelia ofB. cinereaandT. harzianumsometimes gave weak fluorescence with Nile red, and the spores and mycelia ofI. bolleyigave unusually weak fluorescence with Cellufluor. There were other variations of staining among the different dye/fungus combinations, but each fungus showed strong fluorescence with at least one dye. Cellufluor, CMFDA, CMAC and, to a lesser extent, CFDA and Nile red, were efficiently translocated into new growth from preloaded spores or mycelia, whereas FDA, DiIC18(3) and DiOC18(3) were not. The extent of translocation ranged from 0.1 to 1.2 mm in germ tubes arising from spores, and from 0.9 to 9.2 mm in mycelia extending from dye-loaded agar blocks. The findings suggest that fluorescent dyes could be used as markers or tracers in studies of fungal growth and differentiation.