AS A PART of a study of immunity in parapertussis, a survey of the serum agglutinin titers in a representative sample of infants and children was made. Previous observations by Miller,1 in San Francisco, and by Flosdorf,2 in Philadelphia, suggested that the finding of a significant number of persons with agglutinins against Hemophilus parapertussis indicated that the disease caused by this organism had occurred fairly frequently.
The present paper reports the titers of agglutinins for H. parapertussis and for H. pertussis in the serums of 531 patients, from birth through 14 years of age, admitted to the pediatric service of the Strong Memorial-Rochester Municipal Hospitals during the period from Jan. 1, 1951, to July 1, 1952. During this 18-month period, approximately 3,000 admissions occurred. No plan prevailed for the selection of serums to be tested, and they represent a random distribution in relationship to age and time of