The equalitarian co-therapy model which is considered to be the most significant and enduring type of co-therapy relationship is discussed. Co-therapists can interact on at least five occasions outside of the group, and all these interactions have an important effect on the growth and stability of the co-therapy relationship. Co-therapists should not be paired solely on the basis of personal friendship or prior professional acquaintance and factors such as age, sex, race, marital status, personality characteristics, interpersonal style, and the therapeutic situation should be given careful attention. As with many relationships the co-therapy dyad has a period of formation, a period of continued development, a period of stability, and a period of separation. If the co-therapy dyad develops and operates effectively, the group will develop accordingly. Supervision of the co-therapists should be over a unit of two people, the whole of which is more important and more profound than its individual parts. Although there are many limitations to the co-therapy approach, it can add much to the promotion of therapy and the development of group therapists. (RSM/Author)