My thesis investigates the forms, modes and issues associated with the notion of ‘enquiry’ in the discourses and poetics of Émile Zola, Luigi Capuana and Emilia Pardo Bazán. It will do so first by taking seriously the ambition for ‘total enquiry’ in the European naturalist novel around 1880, such as it is considered by Zola’s credo of “tout dire”, by Pardo Bazán’s idea of the “ancha, completa y perfecta” form and by Capuana’s bulimic eclecticism. As a corollary, the reader of the time, in search of “narrative”, experiences an aesthetic practise marked by disciplinary porosity and the diversity of formats and media. Through epistemocriticism, sociocriticism and “historicised semiology”, the aim is therefore to question the relationships between the scientific and the literary, the fictional and the factual, the true and the false, and their epistemological and ideological presuppositions, which the three authors define and redefine in the light of their postures and their specific strategies of affirmation. In line with the disciplinary “decompartmentalization” at work at the time, from the point of view of both reception and production, the assembled corpus brings together novels, chronicles, theoretical and critical texts, but also “scholarly” texts written or consulted by the authors. Through all of these perspectives, this thesis intends to shed light, through a comparative approach, on the historical singularity of an “anxious” enquiry in the last third of the 19th century.