OBJECTIVE: To study the pathological changes and reversibility of the nasal mucosa after drug administration. METHODS: Gentamicin and insulin were dropped into the nasal cavity of rabbits for 3, 5, 7 days to two weeks, after one and two weeks, the nasal mucosa was taken and observed under optical and electron microscopes. RESULTS: It was found that after 3-7 days of drugs administration, damages of the nasal mucosa gradually appeared, and became most serious after one week when the epithelia in some regions detached from basement membr theane. After stopping drug application, the ciliated epithelia restored quickly and completely, goblet cells reproduced and inflammatory reaction disappeared. CONCLUSION: The damages induced by drugs on nasal mucosa are reversible. The intranasal route of drug administration is feasible and promising.