Monto, A. S., J. A. Napier and H. L. Metzner (School of Public Health, Univ. of Michigan, Ann Arbor, Mich. 48104}. The Tecumseh study of respiratory illness. I. Plan of study and observations on syndromes of acute respiratory disease. Amer J Epidem 94: 269–279, 1971.—A study of respiratory infections in the community of Tecumseh, Michigan began in November 1965. Representative segments of the population were defined and families randomly selected for surveillance. They were contacted weekly for a report on occurrence of acute illness, specimens for microbial isolation were collected when respiratory illness was reported, and blood specimens were obtained at set intervals. Families remained on surveillance for one year and were then replaced. Participation in the study was excellent, with 86% of recruited families remaining through the year of surveillance. Families represented a cross-section of the community. During the first 190 weeks of the study, a total of 11,308 respiratory illnesses were reported. Illnesses were divided into syndrome categories on the basis of symptoms; the frequency of the syndromes varied according to age. Severity of an illness was assessed by considering duration and the occurrence of fever and activity restriction.