Improving forage production for an expanding livestock population is essential in the Cukurova and GAP (South-eastern Anatolia Project) regions of Turkey. Feed shortages, especially evident during winter, can be alleviated by introducing high yielding common vetch (Vicia sativa L.) cultivars into crop rotations. The objectives of this research were to determine the genotype x environment interactions and stability parameters for hay yield of 15 vetch lines and cultivars. The vetch genotypes were evaluated in the Cukurova (2 locations for 3 years) and South-eastern Anatolia (1 location for 2 years) regions. In the South-eastern Anatolia region, the rainfall limits plant growth, while the Cukurova region has much better soil and climatic conditions. Since local climatic variation is significant, each location in each year is treated as a separate environment, to give 8 environments. Linear regression techniques were used to analyse genotype x environment interactions (C x E). The hay yield was significantly different between genotypes and environments. while a genotype x environment interaction was present. The variation amongst environments was highly significant, and the mean hay yield ranged from 7453 kg ha(-1), in Dogankent (2002-03), to 2687 kg ha(-1), in Balcali (200304). The genotypes V7' and V12% which had regression coefficients significantly greater than 1.0 and produced mean hay yields above the overall mean, were well adapted to favourable environments. Three entries (V5, V9, and V10) possessed regression coefficients significantly less than 1.0, with hay yield above the grand mean, suggesting that these genotypes were better adapted to poor environments and insensitive to environmental change. Our study demonstrated that previously selected genotypes and cultivars can be successfully grown and make a significantly positive contribution to animal husbandry in the Cukurova and Southeastern Anatolia regions.