This article purports to examine the issue of literary valuation (and/or the values that constitute it) in five prefaces belonging to five poem books from the early 20th century. To do so, we'll rely theoretically on Johnathan Culler's and Wellek & Warren's reflections on value, and on Gerard Genette's work on paratexts. The set of prefaces chosen for analysis consists, in accordance with the working typology, in three alographic authentic prefaces: Olavo Bilac's for Os Bandeirantes by Baptista Cepellos (1906); Euclides da Cunha's for Poemas e cancoes by Vicente de Carvalho (1908); and Vicente de Carvalho's for Ementario by Gustavo Teixeira; and also in two authentic authorial prefaces: Luiz Murat's for Poesias escolhidas (1917) and B. Lopes' for Helenos (1901). Finally, it is concluded that, although these prefaces stand in opposition to the simple mechanical reproduction of literary models already consecrated, the collective mechanisms of work’s validation imposed limits to its possibilities of assigning value to the prefaced text, limits that, in turn , motivated the return to certain bases of value attribution, as the poetic form and the affiliation to the classic literary past.