Single leaf photosynthetic rates and various leaf components of potato (Solanum tuberosum L.) were studied 1-3 days after reciprocally transferring plants between the ambient and elevated growth CO2 treatments. Plants were raised from individual tuber sections in controlled environment chambers at either ambient (36 Pa) or elevated (72 Pa) CO2. One half of the plants in each growth CO2 treatment were transferred to the opposite CO2 treatment 34 days after sowing (DAS). Net photosynthesis (Pn) rates and various leaf components were then measured 34, 35 and 37 DAS at both 36 and 72 Pa CO2. Three-day means of single leaf Pn rates, leaf starch, glucose, initial and total Rubisco activity, Rubisco protein, chlorophyll (a+b), chlorophyll (a/b), alpha-amino N, and nitrate levels differed significantly in the continuous ambient and elevated CO2 treatments. Acclimation of single leaf Pn rates was partially to completely reversed 3 days after elevated CO2-grown plants were shifted to ambient CO2, whereas there was little evidence of photosynthetic acclimation 3 days after ambient CO2-grown plants were shifted to elevated CO2. In a four-way comparison of the 36, 72, 36 to 72 (shifted up) and 72 to 36 (shifted down) Pa CO2 treatments 37 DAS, leaf starch, soluble carbohydrates, Rubisco protein and nitrate were the only photosynthetic factors that differed significantly. Simple and multiple regression analyses suggested that negative changes of Pn in response to growth CO2 treatment were most closely correlated with increased leaf starch levels.