The periodontal ligament of rat molar teeth was observed with scanning electron microscopy (SEM) using two different methods: NaOH maceration and KOH-collagenase treatments. Rat jaws with molar teeth were fixed, demineralized with 10% EDTA, and cut into several pieces. After maceration with 5% NaOH for 5 days at room temperature, the cellular elements were completely removed and the periodontal ligament fibers appeared as bundles of collagen fibrils. The fibers branched and anastomosed but did not spread fibrils randomly. In some regions near the alveolar bone, collagen fibrils circularly binding the fibers were found. When treated with 30% KOH for 7 to 10 minutes at 60 degrees C and with 0.1% collagenase, the periodontal ligament fibers were removed and the cells appeared as spindle and stellate shapes, and combined with the irregular cell processes of each other. Thus, the interaction between the periodontal ligament fibers and cells were three-dimensionally visualized by using the two different methods.