Objective: The purpose of this investigation was to test the microleakage of 3 porcelain repair systems intended for intraoral resin-to-porcelain and resin-to-metal bonding by autoradiography. Method and Materials: Sixty alloy and 60 porcelain disks (10-mm diameter and 2-mm thickness) were prepared. Manufacturer's directions were followed for surface treatment of specimens. Each repair material was applied on 20 alloy specimens and 20 porcelain specimens. Specimens were thermocycled by dipping them in water for 1 minute at 4 +/- 2 degrees C and 58 +/- 2 degrees C for 500 cycles. Leakage was demonstrated by the presence of radioactive isotope at the interface between the repair material and the alloy (or porcelain) as registered by autoradiography. Before testing, specimens were stored in distilled water at 37 degrees C for 24 hours and then thermocycled. Mann-Whitney U test was used to identify the differences. Results: For the alloy groups, differences between Newbond/Clearfil Lustre and GoldLink 2/Ultrabond were significant (P < .05). For the ceramic groups, differences between Cerinate Prime/Ultrabond, Clearfil Lustre/Newbond, Cerinate Prime/Ultrabond, and Silibond/Charizma were significant (P < .05). Conclusions: For the porcelain groups, the amount of microleakage in Ultrabond/Cerinate Prime was significantly higher than the other groups. For the alloy groups, all samples showed leakage.