Nuclear bodies are proteinaceous structures containing ribonucleoproteins found throughout the cell nucleus. The presence of simple and complex nuclear bodies in fragments of periodontal ligament obtained from 10 teeth and in fibroblast-like cells cultured from the same specimens was studied. Nuclear bodies were seen in fibroblasts and less commonly in endothelial cells from all periodontal ligament specimens in vivo and also in periodontal ligament fibroblasts cultured in vitro. The majority of the nuclear bodies were of the simple type, viz. spherical, filamentous and surrounded by a clear halo. Complex nuclear bodies were also identified, mainly in fibroblasts. They were spherical and surrounded by a filamentous capsule but their core was granular or filamentous and sometimes exhibited a concentric arrangement. Some of the bodies resembled, and were close to nucleoli; others were similar to lipid bodies and were free within the nucleoplasm. Although recent studies have suggested that certain types of nuclear bodies may be involved in active transcription, the function of the nuclear bodies in the periodontal ligament remains unknown.