Environmental and physiological factors can lead to boll loss in cotton (Gossypium hirsutum L.). Boll loss, in turn, may limit the rate of CO2 assimilation. The effects of complete boll removal on the daytime and the nighttime CO2 exchange rates of cotton were investigated in a 10-d study conducted in a controlled environment whole-plant assimilation chamber. All bolls were removed from the cotton cultivar DPL50 when it reached an average hourly daytime CO2 exchange rate of 150 mg C h-1, a growth stage occurring approximately 95 d after planting. Only the bolls were removed, the squares and flowers were retained. The daytime CO2 exchange rate decreased on the day immediately following boll removal (day 4 of the 10-d study). A marked recovery period for daytime CO2 exchange rate occurred from day 8 to 10. Nighttime CO2 exchange rate displayed a decreased loss of CO2 (values became more positive) immediately following complete boll removal and continuing for 2 d (days 4 and 5), after which the nighttime CO2 exchange rate entered a recovery period from day 6 to 10 (when this study terminated). The results indicate that complete boll removal alters CO2 exchange rates during both day and night periods, and that cotton plants can recover from these changes in CO2 exchange rates. This recovery may be important in field situations where boll loss is higher than normal. Plants that lose large numbers of bolls may be only temporarily affected by the loss.