L. perenne cv. S.23 (a late flowering perennial ryegrass), T. repens cv. S.184 (a small-leaved, wild-type white clover) and T. repens cv. Olwen (a large-leaved white clover) were grown in containers in the glasshouse as monocultures and as mixtures of grass and clover. Droughting 28-56 days after sowing reduced the shoot growth of grass and clover monocultures equally, but affected clovers more than ryegrass in mixtures, possibly because the clover had much smaller systems than the grass. Droughting 4-5 mo. after sowing reduced cut-herbage weights (but not total shoot weights) of the clovers more than those of the grass. The small-leaved clover became so small that it almost completely avoided defoliation at the end of drought; the remaining stubble weights were much greater than in control plants. Herbage regrowth of the large-leaved clover was unaffected by previous drought and that of the ryegrass was slightly increased. Regrowth of previously droughted small-leaved clover from the heavy, densely-rooted stubble was twice that of the controls. In previously droughted mixtures, clover regrowth was less suppressed by grass than in continuously watered mixtures. During drought in the field, the clover content of mixed swards might be maintained by frequent defoliation. The competitive ability of clover during drought might be improved by breeding for greater root density and for the ability to adopt a low, defoliation-avoiding habit during dry weather.