Thirty-five extracted single-rooted human teeth were decoronalized, root filled with AH-26 and gutta-percha, and perforated at the apical one third level. Repairs of the lateral perforations were carried out with three materials: amalgam plus cavity varnish, EBA cement, and silver glass-ionomer cement. Negative controls were not perforated and positive controls had unrepaired perforations. The roots were then implanted subcutaneously in rats for 5 days to place the materials in a surgical environment. Following retrieval, the roots were placed in a solution containing 20 microCi/ml of calcium-45 for 7 days to measure microleakage. They were rinsed, sectioned, and autoradiographs of the repaired perforations were made. The autoradiographs were projected onto a screen and the extent of penetration of the radioisotope measured. Statistical analysis showed that the EBA cement group exhibited significantly less leakage than the silver glass-ionomer cement group (p < 0.05). No differences were found between the other groups. It was concluded that EBA cement provides a superior seal in lateral root perforations to silver glass-ionomer cement while amalgam was intermediate between the two.