Four mutants with delayed leaf senescence were selected from seed of durum wheat mutagenized with ethylmethane sulphonate. Changes in net photosynthetic rate, efficiency of photosystem II and chlorophyll concentration during the maturation and senescence of the flag leaves of both mutant and parental plants were determined under glasshouse conditions. The four mutant lines maintained photosynthetic competence for longer than the parental line and are therefore functionally 'stay green'. The mutant lines also had higher seed weights and grain yields per plant than the parental line.