The relation between the defensive reactions of the pulp and he depth of the carious lesions are examined, to understand how and which inflammatory and immunocompetent cells infiltrate the pulp in association with the development of carious lesion in order to elucidate the pathogenesis of dental caries, especially from viewpoint of conservative treatment of pulp disease. In this study we have analyzed 150 teeth with different stages of progression of the carious lesion. The condition of the pulp was classified into five groups according to the progression of the carious lesions from stages S0 (non-carious teeth) to S4 (exposed pulp). Cells were identified with indirect immunoperoxidase technique using monoclonal antibodies reactive to pan-T lymphocytes, helper (CD4), suppressor (CD8) lymphocytes, B-lymphocytes (CD20), macrophages (CD68) and dendritic cells (HLA-DR). A few scattered positive T lymphocytes, dendritic cells and macrophages were observed in unaffected pulp with suppressor (CD8) lymphocytes being predominant. In S1 and S2 the number of the analyzed cells was markedly increased and a focal accumulation of mononuclear inflammatory infiltrate can be detected, with the ratio of CD4/CD8 0.22 and 0.23, respectively. The ratio of B/T lymphocytes was 0.21 and 0.24.  Higher numbers of T, CD4, CD8, CD68, HLA-DR and B-lymphocytes were observed in S3 with a CD4/CD8 ratio of 0.84 and B/T lymphocytes ratio was 0.57. In the group with exposed pulp a high ratio of CD4/CD8 and B/T lymphocytes was observed (1.22 and 1.81), showing signs of irreversible pulp inflammation. This study suggests that immune mechanisms play important role in pulpal infection resistance. Results obtained in this study suggest about the regulatory functions of helper (CD4) and suppressor (CD8) lymphocytes as well as the interaction of T and B lymphocytes and their products in the pathogenesis of pulpal disease.