The CO 2 gas exchange of Carica papaya and C. quercifolia was studied under different chilling treatments. After 4d in a low temperature regime (15°C day/5°C night) photosynthesis reduction was more pronounced in C. papaya (15% of control at 25/15°C) than in C. quercifolia (42% of control). Stomatal conductance reduction was similar in both species (25–30% of the control), indicating that CO 2 fixation was more affected in C. papaya, which showed higher intercellular CO 2 levels under stress. Photosynthesis versus intercellular CO 2 -response curves under non stressing conditions were very similar in both species, but differed significantly after 4d in the 15/5°C regime. Under these conditions, gas-phase and mesophyll resistances increased 300% or more in C. papaya leaves. C. quercifolia exhibited a similar increase in gasphase resistance, but mesophyll resistance increased only 80%. The photosynthetic apparatus of C. papaya revealed no capacity to acclimate to low temperatures and a slow recovery after chilling. On the contrary, C. quercifolia apparatus was capable of fast recovery and is able to acclimate and function normally in low temperature regimes.