Hyperventilation is defined as ventilation in excess of that required to maintain normal blood $PaO_2$ and $PaCO_2$. It is produced by several distinct causes: anxiety, respiratory alkalosis, increased blood catecholamine levels, and a decrease in the level of the ionized calcium in the blood. The dental fears about acute pain, needle, drill and dental surgery lead to the severe anxiety and increased blood catecholamine level. Therefore, the most dental patient should be cared gently as the stress reduction protocol. In spite of the gentle care, two cases of hyperventilation were occurred during local anesthesia for incision and drainage of acute odontogenic infectious lesions. We suggest that the dental patients with acute odontogenic infection must be attention for the manifestation of hyperventilation, especially in the medically compromised conditions.