Previous studies have shown that lateral condensation of gutta-percha and sealer can provide an adequate apical seal. The purpose of this study was to compare the level of apical dye penetration when different sealers were used. One-hundred twenty-five teeth with single root canals were biomechanically prepared using the step-back technique and irrigation with EDTAC and 1% NaOCI solutions. The teeth were divided into five groups of 25 teeth each. The control group root canals were filled with laterally condensed gutta-percha and no sealer and the other four groups were filled with laterally condensed gutta-percha and either Apexit, Sealapex, Tubli-Seal, or AH26 sealer. After storage in 100% humidity at 37°C for 48 h, the root surfaces were coated with nail varnish (except at the apex) and placed in 2% methylene blue dye solution and centrifuged at 3×g for 3 min. The roots were sectioned transversely at 1-mm intervals to determine the following mean levels of dye penetrations: Apexit, 1.67 mm; Sealapex, 2.28 mm; Tubli-Seal, 1.95 mm; AH26, 0.82 mm; and gutta-percha alone, 8.37 mm. This study demonstrated that a root canal sealer should be used in conjunction with laterally condensed gutta-percha and that AH26 sealer provides a significantly better apical seal than the other sealers.