The association of severe psoriasis with HIV infection, which dysregulates and destroys the human immune system, supports the hypothesis that psoriasis is an immunologically mediated disease. Psoriasis and Kaposi's sarcoma share angiogenesis as basic early findings and could both be caused by differential cytokine expression or responsiveness. AIDS and research models including transgenic mice offer new models in which to study the role of the immune system and specific gene products in the pathogenesis of psoriasis and other skin diseases.