A fluid filtration system was used to compare the apical microleakage of roots filled with the system B (Analytic Technology), single-cone technique, lateral condensation, vertical condensation, and Thermafil (Caulk-Dentsply). After preparation of the canal system with a Profile (Caulk-Dentsply) five groups of 10 single-rooted teeth were randomly filled according to 1 of the 5 techniques. Phosphate-buffered saline was forced under a 15 cm H 2O pressure, through the apex, toward the coronal part of the root. The filtration rate in L s −1 Kpa −1 was recorded 24 h after filling and after 1-month storage in phosphate-buffered saline. The 24 h results showed that the single cone technique provided the highest leakage (p = 0.001). At 1-month system B, Thermafil and vertical condensation had less leakage than the two other techniques (p = 0.0001): lateral condensation produced moderate apical leakage, whereas the single cone technique showed the highest leakage. Regardless of the technique the apical leakage increased after 1-month storage (p = 0.001 or p = 0.0001, depending on the technique).