Pre-treatment Serum Beta 2-microglobulin (S B2-m) and OKT4/OKT8 Ratio (T4/T8 R) were studied in 15 patients with Mycosis Fungoides (MF) and in 10 subjects with Chronic Superficial Benign Dermatitis (CSBD) in order to verify whether these parameters may lend support to an earlier differential diagnosis. S B2-m levels and T4/T8 R showed no significant difference in CSBD as compared to normal controls. MF patients displayed elevated S B2-m and T4/T8 R values in comparison to healthy controls and subjects suffering from CSBD (P less than 0.001). After photochemotherapy (PUVA), markedly decreased S B2-m and T4/T8 R values were observed in all patients but two who proved to be unresponsive to PUVA treatment. On the basis of reported data, S B2-m and T4/T8 R can be regarded as an additional tool to discriminate CSBD and MF when clinical and histological features are not significantly diagnostic. Finally, these parameters seem to provide reliable information in monitoring response to treatment.