The effects of short periods of water shortage on the CO 2 and water vapour exchange of attached cassava (Manihot esculenta Crantz 'M Col 72') leaves were measured. Gas-exchange and leaf water potential measurements were made in outdoor grown plants previously subjected to varying periods without water. Leaf water potentials fell to between −0.61 and −1.06 MPa and net photosynthesis and transpiration rates declined as leaf water potential decreased. Estimations of the leaf internal CO 2 conductance indicated that the linear relationship established between leaf water potential and net photosynthesis is dominated by, but not completely explained by, stomatal closure.