The present paper deals with one of the Basque relativization strategies: the zein relative, in which an interrogative pronoun, usually zein ‘which’, heads the subordinate clause. The goal is to analyze its use in the 16th to 19th century texts. I set aside the question of whether it was modeled on the syntax of neighboring Romance languages, and focus instead on the analysis of texts and properties of the construction. First, I describe the occurrences of the construction since the earliest texts to the 19th century, including, apart from printed sources, also private letters. Then, I analyze several grammatical properties of the zein relative: the form of the pronoun, the use or lack of subordinating affix, arguments that tend to be relativized or the complexity of the subordinate clause. I try to show that zein relative was not a "barbarism" or alien element not integrated in the grammar, but rather a construction just like any other (even though it did not spread to all registers), with its specific functions and contexts of use.; Lan honen helburua XVI-XIX. mendeetako testuetan izenordain galdetzaileekin egiten den erlatiboaren erabilera aztertzea da. Egitura erromantzeetatik mailegatua den ala ez galdera albo batera utzita, bere erabilera eta ezaugarriak interesatzen zaizkit lan honetan. Hasteko, erlatiboak testuetan dituen agerraldiak iruzkintzen ditut, lekukotasun zaharrenetik XIX. mendera arte. Testu inprimatuez gain, XVI-XVIII. mendeetako gutun pribatuak ere kontuan hartzen ditut. Bestalde, egituraren ezaugarri batzuk deskribatzen ditut: izenordainaren paradigma, menderagailuaren erabilera, erlatibizatzen diren argumentuak, perpausaren konplexutasuna, etab. Oro har, ondorio nagusia da zein erlatiboa, erregistro guztietara zabaldu ez zen arren, ez zela "barbarismoa", hizkuntzaren parte ez den kalko arrotza, bere toki nahiko zehatza eta funtzio propioak zituen egitura bat baizik.