Transparency is a principle that has attracted a good deal of international attention in recent years, especially in connection with combatting corruption and building open, participatory governments accountable to their citizens. Public libraries and archives are not only information suppliers, but also public bodies obliged to provide the citizenry with information about their own governance and activities. Those obligations are laid down in Spanish Act 19/2013 of 29 December on Transparency, Access to Public Information and Good Governance (Spanish initials LTAIPBG). This article describes the results of applying a transparency measuring tool, TransPa_BA, to 106 regionally administered national historic archives and national public libraries. The tool, in turn the result of a research project, includes 20 indicators to measure active public disclosure by public libraries and 22 by archives in keeping with the provisions of the aforementioned Act. The indicators and their respective parameters (visibility, content, form, accessibility, reusability, dating and currency) provide guidelines to enable these institutions to comply with transparency and accountability requirements by furnishing society in general and their stakeholders in particular with information on their activities and performance in key areas. Further to the findings, the target institutions have made hesitant attempts to enhance transparency with respect to earlier inquiries. Public libraries are observed to be more active than archives, although the transparency scores obtained are low due to the failure to provide information on some indicators as well as on parameters such as dating and reusability. Both types of institution have a long road ahead in the pursuit of greater transparency.