For several years, the government of Ontario has undertaken to foster and develop experimental systems for the delivery of primary health care in the province. At the same time, the government wished to devise a strategy whereby the new health care programs could be rigorously evaluated. A Task Force on Evaluation of Primary Health Care Services produced a plan which yields quantitative information about the function of primary health care units. Three essential indexes of performances, comprising categories of Utilization and Financial Performance (UF-Index), Availability, Accessibility and Scope of Services (A-Index) and Quality of Care (Q-Index), were designed. Two additional quantitative indexes, Consumer Satisfaction and Health Professional Satisfaction, were proposed. The derivation and determination of the three essential indexes are provided in the paper in detail, along with acceptable criteria for performance and methods for comparing the performances of different types of practices in different kinds of population.