The literature relative to this form of pollen sensitivity is so meager that one gets the impression that it is an uncommon cause of hay fever. However, one often encounters positive skin reactions to plantain pollen during routine testing. There exists, therefore, an evident discrepancy between the number of cases showing skin sensitivity and those exhibiting clinical hay fever to this pollen. The present study was undertaken (1) to clarify this apparent paradox, (2) to determine definite methods of establishing the clinical diagnosis, (3) to ascertain both the incidence and the importance of plantain hay fever and (4) to study the antigenic relationship of the clinically important species of the plantain family. The plantain family consists of three genera and about 225 species.1The most important genus is Plantago, of which there are about 200 species, only twenty of which are found in the United States. The only species