Three types of nuclear bodies were identified in the Paneth cells of rat small intestine: simple nuclear bodies (type I), small complex nuclear bodies (type III) and large complex nuclear bodies (type IV). The entire simple nuclear bodies and the capsules of complex nuclear bodies were composed of 5 nm filaments. The core of small complex nuclear bodies resembled the interchromatin, while the core of large complex nuclear bodies resembled the granular and fibrillar components of the nucleolus. The Paneth cells of the rat small intestine were found to be especially rich in nuclear bodies: about 80% of nuclear profiles contained one or more sections through nuclear bodies. We suggest that a large number of nuclear bodies in Paneth cells is related to a high rate of protein synthesis in these cells.