RESUMEN
The kinetic changes in morphology and cellular density of epidermal Langerhanscells (LC) in the guinea pig were observed by ATPase cytochemical staining techniqueafter repeated skin application of 5%,3% and 1% of benzalkonium bromide (BB,primary irritant) and 0.05% dinitrochlorobenzene (DNCB,allergen) respectively.We have found that there was a significant difference in the density and morpho-logical change of LC between BB and DNCB application.Treatment with 5% BBcould induce a reversible decline in LC density and changes in cell processes,andwith 0.05% DNCB,the number of LC was decreased and the ATPase activity wasweakened only in the late stage of treatment.The significance of using the kineticchanges in morphology and cellular density of LC as the criteria for the safetyevaluation of weak allergens and weak primary irritants as well as cosmetics wasdiscussed.