Biopsies from 6 patients with AIDS and Kaposi's sarcoma (KS) in the tumour stage, and 6 healthy controls, were immunohistologically examined for the presence of tissue-bound tumour necrosis factor alpha (TNF alpha) and interleukin 6 (IL-6) in the skin. TNF alpha was demonstrated using specific polyclonal antiserum to human recombinant TNF alpha. IL-6 was visualized indirectly using a polyclonal antiserum to partially purified human crude supernatants of activated human blood monocytes, followed by absorption with recombinant human IL-6. The cytokines were found identically located in epidermal cell membranes in stratum granulosum and spinosum of the epidermis from unaffected skin in both AIDS patients and in controls. Biopsies from KS elements showed markedly increased epidermal staining for both TNF delta and IL-6. It was not possible to detect TNF alpha or IL6 in the endothelial cells of the tumour. The observation of increased amounts of epidermal-bound TNF alpha and IL-6 in AIDS-related KS elements supplements previous studies indicating that the skin plays an active immunoinflammatory role in patients with AIDS.