The study examines the individual stages of the naturalistic and psychological novel against the backdrop of the development of medicine and psychology. Through the analysis of selected works by Zola, Barbey d'Aurevilly, Huysmans, Maupassant, and Bourget, the author demonstrates that the notion of an abrupt break with naturalism must be abandoned. The strong presence of both medical and psychological themes in all texts indicates a significant intertwining of both types of novels, as well as a gradual abandonment of scientism, with Zola having shared in the distancing from naturalism that is most pronounced in Bourget's later works.