In vivo and in vitro T-cell-activating ability of murine epidermal cells (EC) was investigated in acutely barrier-disrupted skin by extraction of epidermal lipids with acetone or removal of corneocytes by tape stripping. Contact sensitivity (CS) to 2,4-dinitrofluorobenzene (DNFB) and picryl chloride (PC1) and contact photosensitivity (CPS) to tetrachlorosallcylanilide (TCSA) were significantly augmented when challenged or sensitized at sites treated with acetone 24 h before, compared with the intact skin. CS to DNFB was also enhanced by tape stripping, but not by water rubbing, suggesting that physical stress or a toxic effect of acetone was not responsible for the augmentation. Semi-quantification of TCSA-EC photoadducts showed markedly increased permeability of hapten in the epidermis 24 h after acetone treatment. Bioactive IL-1α was more pronounced in barrier-disrupted than in intact skin. Lymph node T cells from PC1-sensitized mice proliferated significantly more in a hapten-specific and co-stimulatory molecule–dependent manner in response to trinitro-phenylated (TNP) EC from acetone-treated skin than to those from untreated skin. Immunofluorescence staining of epidermal sheets and flow cytometric analysis of dispersed EC showed that subpopulations of Langerhans cells (LC) in acetone-rubbed or tape-stripped skin expressed major histocompatibility complex class II CD54 and CD86 molecules at levels higher than the rest of LC and LC from water-treated or untreated epidermis. Therefore, not only increased permeability of hapten through the epidermis but also altered immune functions of EC potentiate T-cell activation in acute barrier disruption. Such augmentation of immune reactivity may be critical to elimination of environmental noxious agents that penetrate easily into the barrier-disrupted epidermis.