This protocol serves to determine the integrity of the barrier function of (murine) epidermis. Defects in the barrier function lead to dehydration and infection in neonatal mice/humans. One possible way to assess epidermal barrier integrity is by a dye penetration assay as described hereunder. This assay should be done on unfixed, untreated tissues (e.g. formaldehyde- or glutaraldehyde-fixed) or on whole mouse embryos (E18.5). This protocol was adapted from Hardman (1998).