The 1980-81 epidemic of influenza A/Bangkok 79 was responsible for increased absenteeism (1.7 times the rate for the corresponding period of the subsequent nonepidemic year) among selected hospital staff in Winnipeg's Health Sciences Centre. Retrospective study of employment records for 25 of the centre's largest departments showed excess sick-leave costs of about $24 500 during the 2-week period of peak absenteeism that included the epidemic. Although the centre was sampling prospectively for the virus the first positive results became available too late for chemoprophylactic measures to have been effective. The greater increase in absenteeism among nursing staff caring for patients with chronic respiratory disease and nurses working on general medical or pediatric acute infection/isolation wards suggested that these groups be targeted for influenza vaccination in hospitals.