Respiratory symptoms are frequent after bone marrow transplantation (BMT). Most studies focus on lesions of the lower respiratory tract. However, sinusitis is also common in this setting, especially after allogeneic BMT. The nasal respiratory epithelium is the first line of airway defense and is very similar to the bronchial epithelium, especially in terms of ciliary beat frequency and ultrastructural pattern of ciliated cells. We have prospectively studied the nasal respiratory epithelium of 20 marrow recipients (four autologous, 16 allogeneic) with or without sinusitis, by brushing and biopsy of the median turbinate between 2.5 and 148 months after transplant. Samples were studied for ciliary beat frequency, cytology, ultrastructural pattern and HLA-DR expression. We found that 17 of our 20 patients had abnormalities of their nasal epithelium, mainly consisting of either squamous metaplasia or heterogeneous axonemal defects of peripheral and central microtubules. No relationship between these findings and the presence of acute or chronic sinus infection, previous irradiation, graft-versus-host disease or immunosuppressive therapy could be demonstrated in this preliminary study. These abnormalities probably have multiple causes. Prospective studies are needed to determine the respective roles of treatments, infections and immune disorders associated with BMT in these abnormalities, and to know their natural evolution over time and their impact on the occurrence of upper or lower respiratory tract infections.