A clinical controlled trial was designed to determine the impact of Automated Multiphasic Health Testing on morbidity and attitudes. Three strata comprising 574 families (lower-income group enrolled in health maintenance organization, lower-income not enrolled in such a project, and a middle-income group employed by a utility company) were interviewed to obtain information on utilization, morbidity, health status, and attitudes. Sixty percent of adults in each stratum were then screened. All families were interviewed again one year later. The only significant difference found between screened and non-screened subjects was an increase in nights hospitalized for screened subjects. Physicians were interviewed to determine what abnormalities were found and what treatment was required for project and privately referred patients of these physicians. Previously unknown abnormalities prompted retesting for confirmation in only 28 per cent of the cases and even less often led to treatment.