AbstractStomatal behaviour, transpiration and nitrogen fixation were investigated inMedicago sativaL. (cvs. Tierra de Campos and Aragon, Hidalgo‐Maynar 1966),Trifolium repensL. (cv. Aberystwyth S‐184) andTrifolium subterraneumL. (cv. Clare) subjected to drought by withholding water and then to three days’ recovery after rewatering. Dawn leaf water potential was measured with pressure chamber, stomatal response with a diffusion porometer and nitrogen fixation by using acetylene reduction technique.At low water potentials, the leaf resistance was higher inMedicagothan inTrifolium. As water stress developed all species decreased their transpiration,T. subterraneumbeing the one most affected by moderate deficits. During water stress ‘Tierra de Campos’ always maintained higher acetylene reduction levels than ‘Aragon’ and theTrifoliumspecies, except for the lowest water potentials.During recovery from water stress only ‘Tierra de Campos’ reached predeficit transpiration rates. In ‘Tierra de Campos’ acetylene reduction recovery after rewatering was more rapid and intense than in ‘Aragon’. It is concluded that, of the plants investigated, ‘Tierra de Campos’ was b