Abstract: The present invention concerns the preparation of substantially purified agonist anti-EDAR monoclonal antibodies or isolated monoclonal antibody fragments or antigen binding portions or fragments thereof. The invention further relates to isolated agonist anti-EDAR monoclonal antibodies or isolated monoclonal antibody fragments or antigen binding portions or fragments thereof as well as their use in the treatment of X-linked hypohidrotic ectodermal dysplasia and tooth agenesis. The invention also relates to a pharmaceutical composition comprising said isolated agonist anti-EDAR monoclonal antibodies or isolated monoclonal antibody fragments or antigen binding portions or fragments thereof and to a method of treating X-linked hypohidrotic ectodermal dysplasia and tooth agenesis. Finally, the present invention concerns a pharmaceutical kit comprising said isolated agonist anti-EDAR monoclonal antibodies or isolated monoclonal antibody fragments or antigen binding portions or fragments thereof.