Background: In the skin, it is often difficult to differentiate lymphomas from reactive lymphoid lesions by light microscopic examination. Ohjective: Our purpose was to determine whether immunologic data obtained from mutine-processed specimens could be used to further objective morphologic interpretations. Methods: We conducted an immunohistochcmical staining in 44 cases of benign and malignant cutaneous lymphoproliferative lesions using nine antibodies, including anti-CD3, UCHL1, MT1, MT2, L26, MB2, BerH2, 123C3, and MIB1. Results: 1. Immunophenotyping with anti-CD3, UCHL1, MT1, L26, and MB2 was useful for the diagnosis of T cell or B cell lymphoma. However, these antibodies showed a lack of specificity for neoplastic cells, 2. Antibody to CD56, 123C3 showed positivity in 4 cases of angiocentric lymphoma, but negativity in 8 cases showing angiocentric lymphoma-like pathology. 3. Antibody to CD30, BerH2 showed positivity in all 6 cases of CD30 positive large cell lymphoma, but negativity in 6 cases showing diffuse lymphoma-like pathology. 4. Antibody to Ki-67, MIB1 showed positivity in more than 30% of infiltrating cells in 6 cases of angiocentric lymphoma, 4 cases of diffuse B cell lymphoma, and in more than 60% of infiltrating cells in 6 cases of CD30 positive large cell lymphoma. Conclusion: These observations suggest that immunostaining may provide useful adjunctive information in distinguishing benign from malignant cutaneous lymphoproliferations in paraffin sections. (Korean J Dermatol 1999;37(2): 198-205)