An experiment was conducted to determine if negative associations between yield and fiber quality in cotton (Gossypium hirsutum L.) were due to leaf CO2 exchange rate (CER). A 3-year study evaluated six high-quality genotypes, with two high-yielding commercial control cultivars and a G. barbadense L.cultivar, for CER and stomatal conductance to water vapor (g) across contrasting seasons. Yield, fiber quality, and harvest index (HI) were compared with CER and g measured on the uppermost fully expanded leaf on two occasions between mid-flower and cutout. The results show no significant associations between CER and fiber-quality parameters (p<0.05). There was no association between CER and yield, HI, or stem weight. It was concluded that high-quality lines did not photosynthesize less than the high-yielding commercial check. There was a positive association between HI and yield (p<0.01). An inefficient growth habit as measured by a low HI in at least one high-fiber quality genotype was a possible reason for lower lint yield.