By virtue of its anti-inflammatory and immunosuppressive properties, IL-10 plays a crucial role in several immune reactions, including regulatory mechanisms in the skin. In psoriasis, a common cutaneous immune disease, a relative deficiency in cutaneous IL-10 expression is observed. Several lines of evidence suggest that IL-10 could have antipsoriatic abilities. One pilot and two Phase II trials with sc. IL-10 administration over 3 - 7 weeks in patients with moderate to severe psoriasis have supported this hypothesis. The therapy was well-tolerated and clinical efficiency was found in the majority of patients. Immunosuppressive effects (depressed monocytic HLA-DR expression, TNF-alpha and IL-12 secretion capacity, IL-12 plasma levels and responsiveness to recall antigens) as well as a shift towards a Type 2 cytokine pattern (increasing proportion of IL-4, IL-5, and IL-10 producing T-cells, selective increase in IgE serum levels) were observed. These investigations suggest that IL-10 is of major importance in psoriasis and show that IL-10 administration represents a new therapeutic approach. However, long-term administration of large recombinant protein limits the value of this novel therapeutic approach. As such, neither oral nor topical applications are possible; there is a risk of the development of neutralising antibodies.