The presence of strong sinks for assimilates is thought to stimulate photosynthesis by minimizing photosynthetic end product accumulation in leaves. The rate of assimilate movement from sources to sinks appears important not only in controlling the growth of such sinks but also in influencing the rate of photosynthesis in source leaves. If rates of export are not sufficient to prevent assimilate accumulation in source leaves, rates of photosynthesis reportedly decline. To test this hypothesis all fruit was removed from the cotton cultivar 'DPL50' when it reached an hourly average carbon exchange rate (CER) of 105 mg/h. The CER was determined by the use of a whole-plant assimilation chamber, and starch and sugar levels were determined by high performance liquid chromatography (HPLC). The daily rate of gross C uptake through photosynthesis decreased 8.0% after fruit removal. During this period of decreased photosynthesis there was no abnormal accumulation of sugar or starch in the source leaves. However, starch levels decreased in the top and middle leaf positions but increased in the lower leaf position. Sugar levels for the middle, lower and top leaf positions decreased during the dark period but increased during the light period. These results indicate that the observed decrease in photosynthesis in cotton following fruit removal is not the result of an accumulation of starch or sugar. Therefore, we may conclude that the observed decrease in photosynthesis is likely due to some other mechanism, such as a hormonal or stomatal response, or the accumulation of other assimilates.