The three articles in this issue of a periodical focussed on various aspects of the life and health of children in the tropics concern: (1) immune defenses; (2) interactions between nutrition disorders and infection; and (3) immunity and vaccination. The science of immunology has progressed rapidly in recent years. A brief review of present scientific understanding of immune defenses is presented. It is noted that most public health-oriented research on individual nutritional status points to the existence of interactions between infection and nutrition disorders. Practical aspects of this interaction are discussed. Also addressed is the issue of when, and against which diseases, women, mothers, and children in physiologically difficult situations should be immunized. (RH)