Pollen therapy, as developed during the past two decades, is not a process—it is a study of individual susceptibility to pollen, individual contact with pollen and individual response to specific pollen extracts. Since Duke1has shown that susceptibility to pollen is largely a matter of the relative amount of pollen with which the patient has come in contact and since the patient's response to pollen therapy is influenced by the amount of pollen, success in the study of individual hay fever cases is partly dependent on factors outside the physician's control and often outside his knowledge and experience. It is safe to assume that a large part of the poor results in pollen therapy is due to basic botanic causes. The choice of pollen or pollens to be used in the diagnosis and treatment of a hay fever sufferer is really a question of that patient's daily and seasonal