Only 40-50% of the world's children are correctly vaccinated, and each year about 3.5 million children die or become invalids following illnesses preventable by vaccination. It is hoped that new strategies and simplification of vaccination schedules will permit a rapid increase in vaccination coverage so that the UNICEF goal of vaccination of all the world's children by 1990 will be met. As of June 1987, it was estimated that 45% of children in developing countries excluding China had been vaccinated against tuberculosis, 21% against neonatal tetanus, 30% against measles, 45% against whooping cough, and 44% against polio. Most of the illnesses covered by the Expanded Program of Immunization (EPI) can occur very early in life in developing countries. The World Health Organization recommends that children under 1 year old be considered a target group for vaccination. BCG and an extra polio dose should be administered at birth. The DPT injections and oral polio doses should be administered at 6, 10, and 14 weeks. The measles and, where necessary, yellow fever vaccines should be administered at 9 months. The oral polio dose at birth does not always cause antibody synthesis and is intended to provide temporary protection only. The minimum interval between DPT and polio doses is 4 weeks. There is no maximum interval and no need to restart an interrupted series. Vaccination of mothers against tetanus protects the newborn against neonatal tetanus. Pregnant women should be vaccinated twice at intervals of at least 1 month and with the 2nd dose at least 30 days before delivery. The WHO recommends that the target group for tetanus vaccination be enlarged to include all fertile aged women. In the EPI, all vaccines may be administered simultaneously, with DPT, polio, and BCG before 9 months for children seen for the 1st time. Malnourished children should receive priority in vaccination. Premature infants should be given BCG and a preliminary dose of oral polio vaccine before leaving the maternity hospital. Contraindications to vaccination are exceptional and include high fever, acute disorders, and serious reactions to the 1st DPT dose. BCG may be contraindicated for children with clinical signs of AIDS. Vaccination should be integrated into the daily routine of health facilities and the vaccination status of mothers and children should be determined at each contact with the health center. Mass vaccination campaigns can dramatically increase coverage but are costly and require detailed planning and intersectorial coordination.