Tunicates (Urochordate) belong to Chordata, the phylum which also includes vertebrates, as the most primitive group in phylogeny of the group. In spite of earlier reports about allogeneic recognition in tunicates, molecular basis of it remains unknown. Functions of immuno-potent cells and components of their cytoplasmic granules are not defined, either. Memory in immuno-defense reactions have not been proved. Thus, many immunological problems still remain unsolved in tunicate. However, recent studies about cytokines and hemopoiesis add new aspects to tunicate immunology.