Bacterial flora consisting of Gram-positive and Gram-negative germs, aerobes and anaerobes, is distributed along the digestive tract in varying quantities from zero to a maximum of 10(12)/ml of endoluminal aspirate. This bacterial ecosystem counterbalances with the ecological niche of the host organism and harmonizes with the various digestive, secretory, motor, absorption and sensitivity functions of the entire intestine. This dynamic equilibrium between environment, bacterial flora and host may be interrupted due to a variety of complex reasons, leading to quantitative and qualitative modifications of the normal intestinal microbial flora that can cause Small Intestinal Bacterial Overgrowth (SIBO). SIBO is thus due to an invasion of the small intestine, from the upper part, by pathogenic strains of oro-alimentary origin, and from the lower part by colo-fecal germs through an incontinent Bauhin's valve. These germs alter the normal intestinal functions and give rise to a form of diarrhoea in which the characteristics of malabsorption prevail, with all the inherent diagnostic problems. The diagnostic gold standard is the culture of the duodenal-jejunal aspirate which, being difficult to perform and providing unreliable results, is not easily included in the daily clinical routine. Indirect tests include the breath test, which is widely accepted by patients but burdened by diagnostic doubts on the part of medical personnel. Diagnostic confirmation is therefore greatly conditioned by clinical subjectivity and objectivity, as well as by the response to medical therapy. In cases of declared malabsorption, medical therapy is necessary by means of appropriate diet, prebiotics, probiotics and antibiotics. The difficulty in identifying the specific bacterial population and the part of the digestive tract that is affected indicate the appropriateness of a broad-spectrum antibiotic therapy, capable of eradicating aerobes and anaerobes, preferably with a topical rather than a general action, frequently cause of undesired effects.