In this article we intend to offer elements for an analytical framing to study third-sector, organizations in peripheral countries, particularly by observing their idiosyncrasies. In order to do that, we have carried out a review of literature produced in Argentina in the 1990s in the light of isomorphic forces resulting from distinct actors involved in the process of constitution of the third sector. Those forces can be seen within a peripheral isomorphism that shapes structures, procedures, external relations, and themes approached by third-sector organizations.