The effect of elevated CO2 on ovemight malate accumulatíon in the CAM epiphyte Tillandsia ionantha and the CAM terrestrial species Crassula arborescens was compared. Both species showed an increase in nocturnal accumulatíon of malate with increasing CO2 concentrations. This study is the first to show an increase in nighttime malate accumulatíon with increasing levels of CO2 at near-ambient concentrations in a CAM plant. The results indicate that some CAM plants can respond to increasing levels of CO2 in the atmosphere, potentíally leading to an increase in productívity.