SIR-Psoriasis is a common inflammatory skin disease, possibly induced by a T-cell-mediated autoimmune reaction triggered by bacterial superantigens1. Some transgenic animal models2 and mutations in mice3 mimic certain aspects of psoriasis, but they do not allow study of the role of components of the immune system or exogenous stimuli, namely T cells and superantigens, in the onset of psoriatic lesions. Thus, we searched for a model in which a psoriasiform inflammation could be triggered. Eighteen full-thickness skin grafts were transplanted from clinically uninvolved areas of three psoriatic patients onto mice with severe combined immunodeficiency (SCID), lacking Band T cells as described previously4. Technical manipulations (transplantation, injection) did not alter the state of the grafts as seen in controls treated with repetitive intradermal saline injections. Grafts injected with 3 µ, g of the bacterial superantigen exfoliative toxin showed some of the hallmarks of psoriasis (see table); these included profound epidermal thickening (akanthosis) from hyperproliferating basal keratinocytes, documented by expression of the mitosis-associated Ki-67 antigen, along with increased indentation of epidermis and dermis (papillomatosis) and focal neo-expression of the adhesion molecule ICAM-1 on basal and suprabasal keratinocytes overlying the papillary dermis. This pattern is thought to be characteristic of psoriasis5. When the patients' superantigen-stimulated peripheral blood mononuclear cells were simultaneously injected intraperitoneally, an epidermotropic T-cell infiltrate, positive for the cutaneous lymphocyte-associated antigen, was observed (sec table). Marked T-cell epidermotropism was an exclusive feature of grafts from psoriatic donors simultaneously treated with exfoliative toxin and peripheral blood mononuclear cells. None of these phenomena was noted in 18 transplants from 3 non-psoriatic controls. Our observations document the potential of superantigens to trigger psoriasis in a conditioned environment. This experimental approach should greatly help studies on the pathogenesis of psoriasis. In contrast to