Variation in carbon-isotope composition among and between wheat genotypes was correlated with variation in water-use efficiency in separate pot experiments conducted in spring-summer and in winter. In the main, winter experiment, the water-use efficiencies ranged from 2.0 to 3.7 mmolC/mol H₂O (means of four replicates) while the corresponding isotope effects for leaf material ranged from 1.0225 to 1.0194. ¹³C was more abundant in grain than in leaves and stems. It is suggested that carbon-isotope analysis may be a useful tool in selection for improved water-use efficiency in breeding programmes for C₃ species.