The relationship between sealer penetration and apical microleakage following the use of MTAD as an irrigant in root canal procedures was evaluated. A collection of 120 human teeth was divided into three groups of 40 in each group. The final rinse was varied as follows: group 1 - the final rinse was saline solution, group 2 - ethylene diamine tetraacetic acid and for group 3 - MTAD. Each group was then divided into two subgroups (20 teeth) and filled with gutta percha and either AH Plus or Dorifill sealer. Half of the teeth were selected for dye penetration testing and the sealer penetration in the remaining teeth was evaluated using scanning electron microscope. There were no significant differences between the three irrigants, but there was less dye penetration in teeth sealed with AH Plus than Dorifill. Penetration of the sealer was better in the MTAD and ethylene diamine tetraacetic acid groups than in the saline group. Statistically, there was no significant difference between the sealer penetration into the dentinal tubules and the dye penetration.