Monto, A. S. (School of Public Health, Univ. of Michigan, Ann Arbor, Mich. 48104) and J. J. Cavallaro. The Tecumseh study of respiratory illness. II. Patterns of occurrence of infection with respiratory pathogens, 1965–1969. Amer J Epidem 94: 280–289, 1971.—During the first three and one-half years of the study of respiratory infections in Tecumseh, Michigan, certain repetitive temporal patterns of isolation of infectious agents were found. In two of the years, rhinoviruses were associated with an early fall peak of illness. Respiratory syncytial (RS) virus and parainfluenzavirus type 2 each appeared during a single period in every respiratory season and were not isolated at other times, while parainfluenzavirus types 1 and 3 were recovered intermittently. Mycoplasma pneumoniae was not isolated from November 1965 to July 1968, but subsequently has been recovered occasionally. Rhinoviruses appeared to be important in mild respiratory illnesses of preschool children. Many isolates of RS and parainfluenzaviruses were obtained from older children and from adults, indicating that these individuals may be important in introducing infection into the family. Illnesses associated with viral isolations were categorized according to respiratory syndrome, and severity was evaluated through determination of restriction of normal daily activity. Rhinovirus-associated illnesses were most commonly upper respiratory and activity restriction was low. Type A influenza-associated infections were most commonly lower respiratory and exhibited a high frequency of activity restriction. Illnesses associated with other viruses were intermediate both in level of activity restriction and in syndrome type.