BACKGROUND AND OBJECTIVES: The purpose of our study was to examine the expression of 15-lipoxygenase (15-LO) in human nasal mucosa and to investigate the change of expression of 15-LO and cyclooxygenase-2 (COX-2) as a function of mucociliary and squamous differentiation. MATERIALS AND METHOD: Human inferior turbinates were used and immunohistochemistry with 15-LO and COX-2 antibody was done. Passage-2 normal human nasal epithelial cell culture using air-liquid interface method was performed for 14 days and the cells were divided as retinoic acid (RA)-sufficient and RA-deficient group. Western blot analysis for 15-LO and COX-2 expression was performed on each group on 0, 7, and 14 days. RESULTS: 15-LO expression of mucociliated epithelium was noted in ciliated cells and basal cells, but was not found in goblet cells and secretory acini. In squamous epithelium, the expression of 15-LO was weaker than that in the mucociliated epithelium, but the expression of COX-2 showed no difference between them. In Western blot analysis, 15-LO expression was significantly higher in RA-sufficient culture than in RA-deficient culture and this expression was time-dependent. COX-2 expression was almost same level in RA-deficient culture, but its expression was significantly higher in RA-sufficient culture on 7 and 14 days than on zero day. CONCLUSION: 15-LO and COX-2 may be related to differentiation and development of nasal epithelial cells. However, it is unclear whether this relationship is direct or indirect effect of 15-LO and COX-2. This question remains to be solved.