The optimal schedule for the administration of oral poliovirus vaccine (OPV) can be based on a simple paradigm in which the period of maximum risk from natural infection is balanced by the influence of factors which may affect the immune response to vaccination. Surveillance of paralytic poliomyelitis and seroprevalence data indicate that the maximum risk of wild poliovirus infection in most developing countries occurs between 6 and 24 months of age, suggesting that the primary vaccination series for OPV should be completed as early in life as possible. Although scientific evidence and programmatic considerations provide strong support for the currently recommended schedule of OPV at birth, 6, 10, and 14 weeks of age, as many as 30–40% of recipients may still remain susceptible to poliovirus types 1 and 3 after the fourth dose. Because age-specific gaps in immunity have often been associated with epidemic disease, additional strategies to increase population levels of immunity should be considered as progress continues towards the goal of global eradication of poliomyelitis by the year 2000. Administration of OPV in mass vaccination campaigns has been shown to be highly successful in the virtual elimination of wild poliovirus infections in the Americas, and has been adopted as the strategy of choice for the global initiative. Further studies of other supplemental approaches that may hasten eradication should also be pursued, such as expansion of the routine schedule for OPV to five or more doses, and the combined use of both oral and inactivated poliovirus vaccines.