Abstract:The influence of different plant growth regulators including 2,4-D,ZT, 6-BA and ABA on somatic embryogenesis and the amount of endogenous ABA at different stages of embryogenesis was investigated. The effect of each plant growth regulator changed according to the stage of embryogenesis. The amount of endogenous ABA was rather high in single cell stage, decreased at cell clump and embryogenic cell clump stages and dramatically increased at globular embryo stage. It decreased again as the embryo developed. This change in amount of the endogenous ABA explained very well the difference in the effect of exogenous ABA when applied at different stages of embryogenesis.