This article describes the performance by local health departments of core public health functions. A post hoc analysis based on these essential functions was implemented using the 1994 dataset from a cooperative project with the Centers for Disease Control and Prevention (CDC) and National Association of County and City Health Officials, which involved a survey of the nation's 2,888 local health departments. Applying guidelines for each functional area drafted by the Office of Disease Prevention and Health Promotion/Office of the Assistant Secretary for Health, CDC, and the Public Health Foundation in conjunction with the health officers in five states, a score was created for each core public health function: (1) health-related data collection, surveillance, and outcomes monitoring, (2) protection of environment, housing, food, and water, (3) investigation and control of diseases and injuries, (4) public information and education, (5) accountability and quality assurance, (6) laboratory services, (7) training and education, and (8) leadership, policy development, and administration. The individual and summary scores provide a mechanism to measure and describe the 2,079 local health departments' performance of these core functions and to examine their relationship to several characteristics and practices--planning, administrative units, annual total expenditures, and jurisdiction population size. This article shows that the core performance index is highest for the data function and for local health departments serving a population of 50,000 or more people. In addition, the performance index increases as budget increases and is greater for all eight functions in those local health departments using health planning models such as Assessment Protocol for Excellence in Public Health (APEX-PH), Planned Approach to Community Health (PATCH), Healthy People 2000, or Healthy Communities 2000. These results may be used to facilitate cooperation between local, state, and federal health agencies and the communities they serve; strengthen the core functions at the local, state, and federal levels; and improve public health practice.