Eight patients with cutaneous metastatic melanoma were submitted to high-dose intravenous thymopentin (TP5) treatment for 5 weeks: three patients received 1 g three times a week, three received 1 g daily and two received 2 g daily. Four out of eight patients presented a partial response of cutaneous lesions lasting for 1-7 months, and six remain alive with evidence of disease after a follow-up of 2-7 months. A remarkable histologic observation is the presence of tumour necrosis, which was seen as both single cells and large confluent areas. The majority of lymphoid cells present in the tumour are CD45RO+ and CD4+. The CD4+ cells might play an important role in the anti-tumour immune local response by secreting cytokines and inducing apoptotic and necrotic cell death. This hypothesis seems to be confirmed by the presence of a high number of CD4+ cells around intratumoral vessels, while the presence of endovascular micro-thrombosis provides indirect evidence of cytokine activity. Cellular lysis may be produced by the activity of both CD8+ and CD4+ lymphoid cells. The role of TP5 may be an activation of CD4+ and CD8+ lymphoid cells. Clinical and pathological data indicate that TP5 is able to produce consistent clinical and immunological effects in melanoma patients with cutaneous metastases.