In the clinical setting, gastrointestinal parasites in dogs and cats are frequently recorded. They can cause a series of gastrointestinal clinical signs (like diarrhea, hematochezia, perianal pruritus) that can vary according to each age (Riggio et al., 2013). Indeed, puppies and young animals show more pronounced clinical signs than the adult ones, in which the signs are often more limited. Although several studies report the presence of clinical-pathological alterations during parasitic infestation by hematophagous parasites and hemoparasites (Kottadamane et al., 2017; Thongsahuan et al., 2020; Bonilla-Aldana et al., 2022), the literature has not yet described their role with endoparasites. Although in clinical setting the association of eosinophilia with a parasitic infestation is frequent, the worm burden and the variety of parasitic species that can infest the host make the data on eosinophilia not easily interpretable. Although coprological examination has become a routine examination in small animal clinics, the eosinophilia-parasitosis association often involves, especially in veterinary clinics and low-budget owners, the introduction of antiparasitic therapy without coprological confirmation. The current problem of antibiotic resistance which also extends to antiparasitic molecules poses the need to prospectively study the real link of clinical pathological alterations and in particular the incidence of eosinophilia during infestation. The hypothesis is that the correlation between eosinophilia and gastrointestinal parasites is overestimated with the risk of failing the diagnosis of other diseases that can determine high values of blood eosinophils. The purpose of our work is to find if an association between blood eosinophilia and positivity to endoparasites in dogs and cats can be proven.