This paper gives a brief overview of factors determining evapotranspiration of vegetated surfaces. It indicates which of these factors are sensitive to CO2 enrichment. A qualitative analysis is presented of the impact of large scale climate changes. Data in literature indicate that the surface resistance of vegetated areas may change within the range -25% and +50% if the atmospheric CO2-concentration doubles. The impact of such changes on regional scale transpiration is evaluated using a numerical model in which the interaction between the evapotranspiration and the Planetary Boundary Layer is accounted for. It is concluded that the impact of CO2 enrichment on the transpiration at the regional scale is relatively small for aerodynamically smooth surfaces (between +7% and -11%). For aerodynamically rough surfaces the effects are somewhat larger (between +15% and -21%). © 1993 Kluwer Academic Publishers.