Designed for health services planners and decisionmakers on the local level, this guide describes and explains a relatively low-cost short-term approach by which communities can estimate their needs for ambulatory health care services, determine the adequacy of resources to meet those needs, and understand major factors for improving ambulatory health care service delivery. The guide is one product of a demonstration study of ambulatory health care needs, resources, and priorities conducted in Boston, Massachusetts. Part One discusses the Boston study and briefly describes the basic approach presented in terms of its selection, limitations, and how it can be implemented. Part Two is a detailed description of the basic approach which involves a study comparing the actual use made of ambulatory care visits against use which would be expected from national and prepaid plan utilization experience. Explanations are provided for each of the 17 steps involved in conducting the six phases of the study. Part Three addresses things to consider in conducting the study, such as sources of information, potential problems and how to deal with them, and cost. Five appendixes are included: Data Needs and Availability Summary Chart, Listing of Tables Included in the Boston Study, Sample of Parts of Tables Used to Determine Use of Medical Services in Boston, Sample Neighborhood Profile, and Sample Scheduling and Staffing Needs and Cost Worksheet. (HD)