Aim. To study the qualitative composition, the quantitative content of microorganisms, to assess the viability and functional status of neutrophils in the oral fluid of patients using removable and non-removable DOC. Materials and methods. The present study used a free oral fluid of 100 patients aged 21 to 79 years. The qualitative and quantitative composition of the microflora was determined using the PCR method by means of the Femoflor-16 system (NPO DNA-technology, Russia). Determination of the total number of leukocytes was carried out in Goryaev's chamber, analysis of their viability was carried out with Trypan blue staining. Acridine orange was used to study the indices of lysosomal activity of neutrophils. Oxygendependent metabolism was studied using the Nitro Blue-Tetrazolium (NBT) test, and the phagocytic function was determined by the absorption of latex particles. Results. In persons using dentures, the qualitative and quantitative composition of the microflora of the oral cavity changes. The method of hygienic care of the DOC significantly does not affect the composition of the microflora of the oral fluid of patients. In persons using DOC, a decrease in the total number of leukocytes and their viable forms in the free oral fluid was established. However we registered the stability of functioning of viable neutrophils in patients with removable DOC and a significant decrease in the phagocytic ability and microbicidal oxygen-dependent potential of neutrophils when using non-removable DOC. Conclusion. Foreign body in the form of a removable or non-removable DOC changes the functioning of the factors of congenital anti-infective protection of the oral mucosa, which can lead to the development of infectious complications during dental prosthetics.