The aim of this study was to evaluate regulatory T lymphocytes (Tregs) in the course of allergic contact dermatitis (ACD) and to elucidate the role of IL-10 and TGF-β in Tregs activity. Peripheral blood CD4(+)CD25(+) and CD4(+)CD25(high) cells were determined by flow cytometry in patients with acute disseminated ACD ('ad', n = 36), acute localized ACD ('al', n = 26), and disseminated ACD during remission ('rd', n = 27) as well as in controls (n = 22). Serum levels of cytokines were measured using ELISA. The mean percentage of CD4(+)CD25(+) and CD4(+)CD25(high) cells in patients with ad ACD was significantly higher than in controls (p < 0.01) and the remaining patients (p < 0.05). Both cell populations were significantly elevated in persons with widespread skin lesions (p < 0.05). In ad patients the CD4(+)CD25(+) increased during three weeks of disease, although the significant increase of CD4(+)CD25(high) was noted only in the third week. Patients with ad ACD showed a significantly decreased serum level of TGF-β1 as compared with controls and the remaining ACD patients. IL-10 level did not differ between all groups. The elevated population of CD4(+)CD25(high) cells in ad ACD patients, and its dependence on the extension of skin lesions, suggest a role of Tregs in regulating the course of ACD. The growing Tregs percentages may indicate their peripheral generation during ACD. The development of lesions despite an increased population of Tregs suggests their functional defect. The role of TGF-β1 in the suppressive activity of Tregs cannot be excluded.