Seedlings of Maranthes corymbosa (Blume) and Eucalyptus tetrodonta (F. Muell) were grown with or without CO2 enrichment (700μmol CO2 mol−1 The response of stomatal conductance (g2) to leaf drying, exogenous absclslc acid and calcium ions was investigated in M. corymbosa. Reciprocal transfer experiments were also conducted whereby plants were grown in one treatment and then transferred to the other before g, was measured. Stomatal conductance in M. corymbosa was more sensitive (a greater percentage decline in g2 per unit percentage decline in leaf fresh weight) to leaf water status under conditions of CO2 enrichment compared to ambient conditions. However, the rate of reduction of g2 in response to exogenous abscisic acid was not influenced by CO2 treatment. In contrast, the rate of reduction of g2, in response to exogenous CaCl2 was decreased under conditions of CO2 enrichment. Reciprocal transfer experiments showed that expo sure to CO2 enrichment results in a short-term, reversible decline in g2, as a result of decreased stomatal aperture and a long-term, irreversible decline in g2 as a result of a decreased stomatal density. Seedlings of E. tetrodonta were used to investigate the response of g2 to light flux density, leaf-to-air vapour pressure difference (LAVPD), leaf internal CO2 concentration (C1 and temperature. Reciprocal transfer experiments were also conducted. CO2 enrichment did not influence the pattern or sensitivity of response of g to LAVPD and C in E. tetrodonta. In contrast, the slope of the response of g2, to temperature decreased for trees grown under elevated [CO2]a conditions and the equilibrium g2 attained at saturating light was also decreased for plants grown under elevated [CO2a. conditions.