Influenza B virus infections were documented in Houston, Texas, in 726 patients with febrile respiratory illnesses who presented to representative primary care facilities during the 1976-1977 respiratory disease season. This epidemic followed a "herald wave" of illness associated with influenza B during the preceding spring. Over one-half the virus isolates were from children aged 5-19 years, and school absenteeism rates indicated that about 40 per cent of the students in the Houston area were ill enough to miss school during the epidemic. The rapid rise in the number of cases among students after the school holiday recess demonstrated the importance of school attendance for the rapid dissemination of influenza viruses. During the later phase of the epidemic, most of the cases were preschool children and adults. In addition to disease of the respiratory tract, the epidemic was accompanied by cases of Reye's syndrome at a rate expected for an urban area.