Influenza epidemics are accompanied by considerable excess morbidity and mortality especially among the elderly and the chronically ill. In the influenza season 1995 a controlled, randomized trial was carried out to examine the impact of postal invitations and user fee on influenza vaccination rates. Five hundred and eighty-five patients aged 65 years or older participated. They were all recognized by their general practitioner (GP) to be in the risk group to whom influenza vaccination is recommended. One third were invited to free influenza vaccination. Another third received postal invitations to influenza vaccination paying the usual fee ($40-$60 US). The last third served as a control group, being vaccinated on their own request and paying the usual fee. In the control group 25% (19-31%, 95% confidence interval) of the patients were vaccinated, compared to 49% (42-56%) in the group which received a postal reminder and paid the usual fee, and 72% (65-78%) in the group invited to be vaccinated free of charge.