Ultraviolet-B irradiation of murine skin before contact sensitization alters the antigen-presenting activity of cells in the skin and draining lymph nodes (DLN), decreases the contact hypersensitivity (CHS) response, and induces hapten-specific Ts cells. We determined whether hapten-bearing antigen-presenting cells (APC) from the DLN of UV-irradiated mice induce Ts cells. APC from UV-irradiated, FITC-sensitized mice were isolated, and FITC+ cells were FACS-purified and injected into the hind footpads of naive, syngeneic mice. Unseparated and FACS-purified bright FITC+ cells (FITChi) from UV-irradiated mice induced Ts. However, dull (FITClo) FITC+ cells, T-cell-depleted FITChi cells, or DLN cells from C3H SCID mice failed to induce Ts. Injection of FITC-bearing DLN cells from nonirradiated mice into UV-irradiated recipients failed to immunize and induced Ts instead. Treatment of the UV-irradiated recipients with anti-TNF-alpha blocked these effects. Thus, transferable suppression is due to Thy-1+ cells, does not require UV-altered APC for induction, and may depend on TNF-alpha.