The World Health Organization (WHO) has chosen the theme "Emerging Infectious Diseases--Global Alert, Global Response" for this year's World Health Day to call attention to the threat posed by infectious diseases that have been recently recognized in humans or that are making a comeback. Factors in the emergence and re-emergence of infectious diseases include deterioration of public health infrastructure, increasing microbial resistance to antibiotics, and social and ecological changes associated with human population growth. WHO emphasizes the need for committed partnerships among countries, international organizations, nongovernmental organizations, and individuals to improve disease surveillance and control capabilities in order to prevent and contain epidemics. For its part, WHO is strengthening the existing three-pronged global monitoring system, consisting of the WHO Collaborating Centers in the area of infectious diseases, the antimicrobial resistance monitoring networks, and the International Health Regulations. To adequately confront the problem of infectious diseases in the next century, there is a need for strong national disease surveillance and control programs; global disease monitoring and alert networks; rapid information exchange through electronic links, including the World Wide Web; and effective preparedness and rapid response capability to contain epidemics.