We reported that a cysteine proteinase inhibitor, cystatin α, would act as a barrier in the stratum corneum against Staphylococcus aureus V8. Based on this finding, we attempted to characterize other proteins related with epidermal barrier function. In this experiment, the expression of human bactericidal permeability increasing protein (hBPI), which has found in granulocytes and had a high homology with endotoxin binding protein (lipopolysaccharide binding protein), in epidermis is examined. A peptide, whose amino acid sequence was -L-Q-K-E-L-K-R-I-K-I-P-D-Y-S-D-S-F-K-I-K-H-L-G-K-G-C-, was synthesized and conjugated with keyhole limpet hemocyanin (KLH). The hBPI peptide conjugated with KLH (hBPI/KLH) was injected to rabbits to obtain an antibody. In order to investigate its properties, immunoblotting analysis and indirect immunofluorescence technique using anti-hBPI/KLH antibody were performed. A formation of the specific antibody against hBPI was determined by ELISA using the synthesized peptide without KLH as an antigen. Four protein spots in newborn rat epidermal extract of alkaline 10 M urea solution containing 2-mercaptoethanol and NP-40 were reacted with anti-hBPI/KLH antibody, whose isoelectric points were pH 5.3 to 5.5 and molecular weights were about 55 kd. The similar result was observed in human epidermal extract. The immunofluorescent study using newborn rat or human skin revealed that the cell membrane region of the stratum corneum was reacted positively with the antibody. These findings suggest that hBPI finds in both human and newborn rat epidermis and that it locates in the cell membrane region of the stratum corneum.