In considering the place of Primary Health Care in a comprehensive health system, we must first consider what is meant by the term 'comprehensive'. Comprehensive systems take into account all phases of life from infancy to old age, and integrate all aspects of being, including physical, psychological, mental, social, environmental, political and so on. It is the task of those who deliver the primary health care system to evaluate and prioritize health needs in specific populations, and to implement programs which honor the community's unique priorities, taking into account all phases and aspects of life. Drawing upon data collected from a comprehensive field survey of community health activities in Hiketa, in Kagawa Prefecture in Shikoku, and other similar surveys carried out in Japan, as well as references such as the Report of the International Conference on Primary Health Care (Alma Ata), and the World Health Organization Global Strategy for Health for All by the Year 2000, this background paper will outline the critical aspects to be considered in implementation of primary health care in comprehensive health systems, as a context for further discussion. Aspects to be considered are as follows: Community representation and participation Evaluation of health needs Prioritization of health needs Implementation: consultation with specialists Implementation: utilization of local resources Implementation: health education Implementation: support of local government Implementation: co-ordination of laymen, specialists, officials and others Evaluation Follow through. Illustrative examples will be used to highlight problems and solutions as each aspects is considered.