Ineligible persons include anyone who unlawfully uses or is addicted to controlled substances, has been adjudicated as a mental defective or committed to a mental institution, is an illegal alien, has been dishonorably discharged from the Armed Forces, or has renounced U.S. citizenship. Data were obtained to assess the feasibility of a system to prevent firearms sales to ineligible persons. Each procedure to access data and establish eligibility was assessed in terms of costs, legal and policy considerations, accuracy, completeness and validity of data, time for implementation and individual checks, and the extent to which persons and their ineligibility categories were included in the data base. It was determined that integrating individual data bases into a single system for eligibility verification would raise several issues. Such a system would require that drug treatment centers, courts, commissions and boards with mental health jurisdiction, the Immigration and Naturalization Service, the Defense Manpower Data Center, and the Passport Services Office share relevant records. Such a system would also entail significant startup and operating costs for both the integrated system and the literally thousands of local, State, and Federal agencies that would either share or access the data. Technical and policy issues related to data system feasibility focus on data quality, system configuration, and legal questions. Relevant Federal forms and statutes and State statutes are appended. 51 references and 13 exhibits