The purpose of this study is to evaluate, with the electric pulp tester, the anesthetic efficacy of the periodontal ligament injection using 2% lidocaine with 1:100,000 epinephrine and saline in human mandibular premolars. The periodontal ligament injection using 2% lidocaine with 1:100,000 epinephrine was found to be an effective technique for anesthetizing mandibular first premolars. However, the duration of profound pulpal anesthesia was approximately 10 minutes. The periodontal ligament injection using sterile saline was not an effective technique for anesthesia. Teeth mesial and distal to the injected tooth may also become anesthetized with this injection technique. The initial needle penetration and injection of the anesthetic solution in clinically healthy teeth were only mildly discomforting. No increase in tooth mobility was observed 45 minutes after the periodontal ligament injection. No clinically observable pulpal or periodontal damage was seen at 3 weeks after the injection.