THE EVALUATION MODEL PRESENTED IS BASED ON A SOCIAL SYSTEMS ORIENTATION THAT ASSUMES THAT BROAD SOCIAL FORCES, COMMUNITY PROCESSES, AND HUMAN INTERACTIONS ARE PRIMARILY RESPONSIBLE FOR MENTAL HEALTH AND ILLNESS. THE 5 STAGES IN THE EVALUATION MODEL ARE AS FOLLOWS: (1) DESCRIPTION, CONCEPTUALIZATION, AND DEFINITION OF OBJECTIVES; (2) ASSESSMENT OF NEED AND SERVICES UTILIZATION; (3) COMPARATIVE STUDIES OF NEED WITH SERVICES UTILIZATION AND WITH THE CENTER'S STATED GOALS: (4) OUTCOME APPRAISALS; AND (5) IMPACT STUDIES--INVOLVING EPIDEMIOLOGIC STUDIES, PARTICULARLY FOLLOWUP SURVEYS AND CONTINUING SOCIAL-INDICATOR ANALYSES, TO ASSESS THE QUALITY OF LIFE WITHIN THE CATCHMENT AREA. THE ASSESSMENT OF NEEDS AND UTILIZATION OF SERVICES STUDY DESCRIBED OCCURRED OVER A 5-YEAR PERIOD FROM 1970 IN ALACHUA COUNTY, FLA., TO EVALUATE ITS MENTAL HEALTH NEEDS AND UTILIZATION OF SERVICES. A 317-ITEM INTERVIEW SCHEDULE WAS DEVELOPED TO YIELD COMPREHENSIVE INFORMATION ABOUT FAMILY AND COMMUNITY LIFE AND HEALTH AND ILLNESS. IT WAS ADMINISTERED BY TRAINED INTERVIEWERS TO A RANDOM SAMPLE OF 1,645 RESPONDENTS IN THEIR HOMES. THE SAMPLE WAS REPRESENTATIVE OF THE COUNTY'S POPULATION AS COMPARED WITH THE 1970 CENSUS. OF THE 1,645 RESPONDENTS, 84 PERCENT WERE UTILIZERS OF PHYSICAL HEALTH CARE SERVICES, BUT ONLY 4.6 PERCENT USED MENTAL HEALTH CARE SERVICES. ONLY SLIGHTLY LARGER PERCENTAGES OF WHITES THAN BLACKS AND FEMALES THAN MALES UTILIZED EITHER PHYSICAL OR MENTAL HEALTH CARE SERVICES. MORE OF THE YOUNGEST GROUP, AGED 16-29, UTILIZED PHYSICAL AND MENTAL HEALTH SERVICES THAN THOSE IN ANY OTHER AGE GROUP. MORE UPPER THAN LOWER SOCIOECONOMIC RESPONDENTS USED BOTH PHYSICAL AND MENTAL HEALTH CARE SERVICES. A COMPARISON OF NEEDERS AND UTILIZERS IS COMPARED, AND THE RESULTS OF RELIABILITY AND VALIDITY CHECKS ARE REPORTED. RESULTS OF THE SURVEY ARE GRAPHED. REFERENCES ARE PROVIDED. (RCB)