Abstract: Frozen sections df skin lesions from one case of spitz nevus and two cases of malignant melanoma (MM) were examined by immuno-enzymatic labelling technique and a panel of monoclonal antibodies. Pan T (OKT11⁺) cells were the major inflammatory infiltrates seen in both spitz nevus and MM. The ratio of T helper cells (Leu3a⁺) and T suppressor cells (Leu2a⁺) appeared normal in spitz nevus but decreased in the MM. In the grade IV MM, the inflammatory infiltrates were obviously decreased, meanwhile the percentage of pan T cells and Ia⁺ cells were also decreased, OKT6⁺ cells were absent. However, the percentage of monocytes (Monol⁺) was increased. These results suggest that the im-munohistophenotype of inflammatory infiltrates between the spitz news and MM are different and the cellular immunity is abnormal in the patients with MM.