This study was intended to determine the tissue distribution of lidocaine in mandibular mucosa and alveolar bone marrow after local infiltration. Tissue distribution of local anesthetics shortly after regional injection has been unclear. We used macro autoradiography to visually examine the tissue distribution of lidocaine shortly after local anesthetic infiltration. Male Japan White rabbits received an injection of ¹⁴C-labeled 2% lidocaine with or without 1:80,000 epinephrine. The areas of infiltration and proportion of distribution 1, 5 and 10 minutes after administration were measured. After the administration of 2% lidocaine with 1:80,000 epinephrine, infiltration area increased over time. Ratios of distribution in alveolar bone marrow at the level equivalent to the root apex increased in 1 to 5 minutes after administration, and then decreased. In contrast, after the administration of plain lidocaine, infiltration was hardly detected. These results suggest that infiltration of lidocaine with epinephrine diffused to a wider area over time after administration and then gradually absorbed into the capillaries.