Formulation of the contact allergens dinitrochlorobenzene and isoeugenol in ethanolic liposomes (ethosomes) increases their sensitizing properties in the local lymph node assay compared with an ethanol-water formulation of the allergens. Likewise, isoeugenol and methyldibromo-glutaronitrile formulated in ethosomes enhanced the patch test reactions in sensitized human volunteers. The relationship between the percutaneous penetration/absorption and sensitization/elicitation phases of contact allergy is not well elucidated.