Eight introduced and three local onion ( Allium cepa
) cultivars were evaluated at four locations for two seasons in Kenya to determine genotype x environment interactions and stability for bulb yield and other agronomic characters. The genotype x environment interactions and stability were investigated by regression analysis. Genotypic effects were highly significant for all traits except days to maturity. Bulb yields for the 11 cultivars varied between 16.2 and 35.6 t ha-1
; introduced cultivars out-yielded the local ones. Environment (E) and genotype (G) x environment interaction effects were highly significant for all traits. A considerable portion of genotype x environment interaction effects for bulb yield was linear. The significant G x E (linear) variance indicated that there were genetic differences among the cultivars in their response to the environment.