We studied, by electron microscopy, muscle biopsies from seven patients with autosomal dominant oculopharyngeal muscular dystrophy (OPMD) belonging to the recently described Bukhara-Jewish cluster. Typical tubulofilamentous intranuclear inclusions (INI) of 8.5 nm outer diameter were present in all cases. The INI were observed in 4.5 +/- 1.8% of the nuclei in five patients. In the other two, they occurred in 9.5 +/- 0.5% of the nuclei and often occupied a larger nuclear area. These two patients, offspring of intermarriage between affected cousins, had an unusually severe form of OPMD beginning in their early 30s, suggesting homozygote state. Our results confirm that INI are pathognomonic for OPMD and suggest that their frequency may be quantitatively related to the number of abnormal DNA copies.