Abstract: TDZ(N-phenyl-N’-1,2,3-thidiazol-5-yl-urea) is a substituted phenylurea compound and has emerged as a highly efficacious bioregulant of morphogenesis in the tissue culture of many plant species. Application of TDZ induces a diverse array of cultural responses ranging from induction of callus to formation of somatic embryos.TDZ exhibits the unique property of mimicking both auxin and cytokinin effects on growth and differentiation of cultured explants. The recent app roaches applied to study the morphogenic events initiated by TDZ are clearly beginning to reveal the details of a variety of underlying mechanisms. Various reports indicate that TDZ may act through modulation of the endogenous plant growth substances, or as a result of induced stress. The other possibilities include the modification in cell membranes, energy levels, nutrient uptake, or nutrient assimilation. In this review, several of these possibilities are presented and summarized in light of recently published studies on characterization of TDZ-induce dmorphogenic effects.