The translocation of (14)C-photosynthate in detached blades of sugarcane was studied under illumination from red, green, blue, and cool-white fluorescent lamps; under far-red illumination from the sun, and from incandescent lamps; and in total darkness.The percentage of basipetal translocation and the accumulation against the concentration gradient were stimulated by light from the red or blue lamps more than by green or cool-white fluorescent illumination.Basipetal translocation took place equally well in red light lacking blue irradiation and in blue light. Since the action spectrum for light-induced change in viscosity is a typical blue-type spectrum, the effect of light upon translocation is not due merely to changes in the physicochemical properties of protoplasm.Basipetal translocation took place in red light lacking blue irradiation better than in cool-white fluorescent light, which may suggest a red stimulation of translocation.Illumination in the far-red region of the spectrum did not support basipetal translocation but acted like total darkness.Because of the wide emission characteristics of the fluorescent lamps employed, it is impossible to decide whether a chlorophyll-like system or some other pigment is involved in the light stimulation of phototranslocation.Whatever the activating wavelength and whatever the pigment system involved, these results show that the phototranslocation of sucrose in the phloem is influenced by the quality of illumination.