Seven mexican lines and one american cultivar (0), as well as their testing sites were compared for stability of yield and Yield components. The experiments were established in eight locations (L) for three years (Y). The main effect for genotypes as well as the Y X L interaction were more important than any of the first order interactions. It is suggested that the number of test locations could be reduced as well as the number of years of testing. Three linesd have a higher yield potential than the commercial check variety Deltapine 80; the stability analysis indicated that most regression coefficients were very close to unity, except to the high Yielding ones, but the difference was not significative in general, the deviations from regression were much more smaller for low yielding lines as compared to the high yielding ones, but both groups were not significantly different from zero. On the other hand the study of testing sites showed that the Valle del Yaqui, Sonora, located in the costal region in northwest Mewxico, where the lines were developed, is more sTable for detecting superior genotypes, with high stability and consistency.