The purposes of the present study were to determine the effectiveness of infiltration anesthesia in the mandibular primary molars compared with inferior alveolar nerve block, and how tooth location, and the type of treatment performed, and the volume of anesthetic solution relate to the quality of anesthesia. The study population consisted of ١١٦ cooperative children, ٣-٦ years old, requiring the same type of treatment on contralateral mandibular molars.