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Genotypic variations in leaf gas exchange and grain yield were analysed in 10 highland-adapted quinoa cultivars grown in the field under drought conditions. Trials took place in an arid mountain region of the Northwest of Argentina (Encalilla, Amaicha del Valle, 22°31'S, 65°59'W). Significant changes in leaf gas exchange and grain yield among cultivars were observed. Our data demonstrate that leaf stomatal conductance to water vapour (g s ) is a major determinant of net CO 2 assimilation (A n ) because quinoa cultivars with inherently higher g s were capable of keeping higher photosynthesis rate. Aboveground dry mass and grain yield significantly varied among cultivars. Significant variations also occurred in chlorophyll, N and P content, photosynthetic nitrogen-use efficiency (PNUE), specific leaf area (SLA), intrinsic water-use efficiency (;WUE) and carboxylation capacity (A n /C i ). Many cultivars gave promissory grain yields with values higher than 2000 kg ha ―1 , reaching for Sayana cultivar 3855 kg ha ―1 . Overall, these data indicate that cultivars, which showed higher photosynthesis and conductances, were also generally more productive. Carbon isotope discrimination (Δ) was positively correlated with the grain yield and negatively with i WUE, but δ 15 N did not show significant correlations. This study provides a reliable measure of specific responses of quinoa cultivars to drought and it may be valuable in breeding programmes.