Periodontitis (P) is an infectious disease that develops in the supporting tissues of the tooth. One of the risk factors leading to it may be dysfunction of some immune system cells. Therefore, the object of the study was to assess selected functions of peripheral blood leukocytes in patients with various forms of P. As leukocytes are able to secrete interleukin (IL)-4 and IL-6, concentrations of their soluble receptors and the expression of their membrane receptors were investigated. Twenty generally healthy subjects with agressive (AP) and chronic periodontitis (CP) were enrolled in the study. The control group consisted of 8 healthy subjects, with no changes in periodontium. Peripheral blood mononuclear cells (PBMCs) were isolated and cultured. Levels of IL-4, IL-6, and their soluble receptors sIL-4R and sIL-6R were determined in the supernatant by ELISA. The expressions of cell surface IL-4R and IL-6R were assayed on PBMC using flow cytometry. No statistically significant differences were found in the selected parameters between people with periodontal disease and healthy controls. However, in subjects with AP, there was an increasing tendency in IL-6 concentration and IL-4R expression on PBMCs. Our results show that leukocytes play a significant part in P and their activity is probably lesion-dependent. Estimation of the cytokines secreted by leukocytes may facilitate differentiation and prognosis of the disease progression.