Despite recommendations supporting annual influenza vaccination for people aged 65 years or older, vaccination rates remain low. Several studies have evaluated the effect of sending mailed reminders, but few have compared alternative ways of reminding patients to receive the vaccine. In a randomized trial of 939 patients aged 65 years or older in four family practices carried out between Oct. 23 and Dec. 31, 1984, we compared three ways of reminding elderly patients to receive the vaccine: personal reminder by the physician, telephone reminder by the nurse and reminder by letter. The vaccination rates for the three groups were 22.9%, 37% and 35.1% respectively. No reminder was issued to a control group, and the rate was 9.8%. Some patients could not be reached by telephone, and some did not see the physician during the specified time. Among the patients whom the nurse actually contacted, the vaccination rate was 43.5%; the rate for patients whom the doctor actually saw was 45.1%. Overall, a telephone reminder by the nurse was the most effective method, and at an hourly salary of $16 or less this method would also be the most cost-effective. The reminders used in this study were automatically generated from a computerized medical record system. The study shows how a computerized system can be used to identify patients for whom preventive procedures are due.