question: Background: The peafowl is an ornamental bird that has the habit of eating directly from the earthy soil, which makes thisbird more susceptible to endoparasites. One important endoparasite is Eucoleus contortus, which leads to inflammatoryprocesses that alter the local microbiota, potentializing disease. By the other way, a member of the birds microbiota thereis the genus Lactobacillus, but when occurs some imbalance, these bacteria can overgrowth and even cause some infection.This report describes the pathological and microbiological findings of chronic necrotizing pneumonia and aerossacolitiscaused by Lactobacillus agilis in a peafowl, associated with parasitism by E. contortus.Case: A peafowl (Pavo cristatus), adult, male, who lived on a farm with contact with other species of animal, was submittedto post-mortem examination due to sudden death. This animal lived in an extensive system on the property and was the onlyone of its species. During the gross evaluation, the air sacs were filled with solid yellowish crumbly material. The samematerial was observed forming well-defined nodules that occupied > 50% of the lung parenchyma. Histological analysisshowed multiple parabronchi dilated and filled with caseous necrosis, characterized by abundant cellular debris and fibrindeposition. These areas were surrounded by the proliferation of fibrous connective tissue and inflammatory infiltrate ofmacrophages, giant cells, lymphocytes, and plasma cells. The air sacs parenchyma showed fibrin deposition and mixedinflammatory infiltrate. Multiple gram-positive bacilli were observed within the caseous foci in Gram-stained slides. Inthe crop and esophageal mucosa, cross-sections of filiform nematodes morphologically compatible with E. contortus wereassociated with chronic inflammatory infiltrate and epidermal hyperkeratosis. A lung section was submitted to GramBrown-Hopps and Ziehl-Neelsen...(AU)