An in vitro comparison of apical microleakage of four root canal sealers was performed using a dye leakage/clearing method. Ketac-Endo, Tubliseal (old formula), Tubliseal (new formula), and Roth's 801 cement were compared with a control group of teeth obturated with laterally condensed gutta-percha and no sealer. Teeth were instrumented, obturated, demineralized, and cleared. Linear dye penetration was determined by dissecting microscope. Results were analyzed statistically. All groups obturated with sealer displayed significantly less leakage than the control group. There was no difference between the Tubliseal formulations, and the Ketac-Endo showed significantly more leakage than the three zinc oxide-eugenol-based sealers.