In just under a quarter of a century, the Expanded Programme on Immunisation has been associated with an increase in infant immunisation coverage from around 5% to 80%, and the prevention of at least 3 million deaths annually, at very low cost. The global target of poliomyelitis eradication by the year 2000 appears feasible. Measles is the next likely target for eradication via immunisation, through 'catch-up', 'keep up' and 'follow-up' strategies which have proven highly effective in the Americas. Yet much needs to be done in order to extend readily achievable immunisation benefits equitably to all the world's people and to realise the potential of existing and soon to be available vaccines for disease control and eradication, as experience with yellow fever and hepatitis B vaccines demonstrates. Unsafe injection practices are widespread, have received inadequate attention, and cause a substantial global burden of blood-borne infections. The risk of increasing global inequity in immunisation highlights the centrality of resource allocation priorities in determining the extent to which the benefits of immunisation will be realised, particularly for new vaccines which are significantly more costly than established EPI vaccines. WHO/UNICEF strategies to target more effectively immunisation support to the neediest countries, to prioritise new vaccines, and to target carefully vaccine procurement and encourage sharply tiered vaccine pricing support both equity and sustainability. However, increasing the resources available to immunisation is vital and requires powerful advocacy on public health, moral, cost-effectiveness and legal grounds. More appropriate resource allocation priorities could readily provide the means necessary to address both technical and operational immunisation challenges.