In the D ward of Nagoyashi-Koseiin geriatric hospital (36-beds), upper respiratory illnesses were recognized in all the inpatients between July and August in 1995, and we studied 7 elderly subjects with parainfluenza 3 infection diagnosed by serology and viral culture. The outbreak of upper respiratory illnesses occurred in the ward during the 17 days from July 21 through August 6, 1996. Fifteen of the 18 elderly persons with upper respiratory illnesses were tested by serology; parainfluenza 3 infection was identified in 7. One of the 7 patients, parainfluenza 3 virus was isolated. Seven elderly subjects with parainfluenza 3 infection were 2 males and 5 females and five of them (71.4%) were bedridden. The most common complaint was fever and coughing in 7/7 (100%), followed by sputum in 5/7 (71.4%), wheezing in 4/7 (42.9%). The pyrexial period in the parainfluenza-infected group ranged from 1 to 4 days (average 3.1 days), and was significantly shorter than that of the influenza group. The maximum recorded temperature in the parainfluenza-infected group ranged from 37.0 to 39.2 degrees C (average 38.1 degrees C), and was significantly lower than that of the influenza group. Two of the 7 patients with parainfluenza 3 virus infection had pneumonia, but nobody died, and all 7 patients recovered without sequele. It is possible that parainfluenza 3 virus infection among elderly subjects cause secondary bacterial infection, so we think that prevention of nosocomial parainfluenza infection should be a high priority in the case of outbreak of such an infection in a ward.