Net photosynthetic rate of aquatic carnivorous plants in standing waters can sometimes be limited by low concentration of free CO2. As net photosynthetic rate of terrestrial plants growing in vitro is greatly reduced, as compared to the same plants grown naturally, it could be assumed that photosynthetic CO2 affinity in aquatic carnivorous plants growing in vitro will be reduced. The aim of this study was to compare values of CO2 compensation point of photosynthesis in several strains of Aldrovanda vesiculosa and in 13 aquatic Utricularia species, both in plants growing under nearly-natural conditions in containers or aquaria and in vitro. The dependence of CO2 compensation point on growth conditions is discussed.