To test the effect of light quality on carbohydrate translocation, leaf strips of Phaseolus vulgaris L. cv. Black Valentine were prepared before or after exposure to a 48 h dark pretreatment. Central portions of the strips were labelled with 14CO2 and translocate was allowed to move acropetally and basipetally along the strips. The portions of the strips on either side of the labelling region were exposed to red or far-red light, or darkness. Translocation in darkened strips was predominantly basipetal. When portions of the strips were given red light, translocation to that region was suppressed. It is suggested that Ptr does not promote unloading. Pr formation induced by far-red light, or dark decay of phytochrome, promotes unloading and long distance transport in a high irradiance response, but does not alter the normal polar transport in the strips.