Cytoplasmic microtubules are one of the various components of the cytoskeleton. They are associated with transport of lysosomes and movement of the cell membrane. Augmentations of the lysosomal enzyme activity and chemotactic activity are found in the neutrophils of patients with Behçet's disease, and colchicine which induces microtubule depolymerization is effective in the treatment of this disease. We examined microtubules in the neutrophils of 24 patients with Behçet's disease, by an indirect immunofluorescence technique, to investigate the significance of the microtubules in this disease. The distribution of the microtubules was different between the patients in the exacerbation stage and normal subjects, and also between the exacerbation stage and the remission stage. These results suggested that microtubules play some significant role in the pathophysiology of Behçet's disease.