Purpose: This study aimed to investigate the electrochemical behavior of commercially pure titanium (grade II) coupled with type IV gold alloy and nickel-chromium alloy at different surface area ratios in 3 different electrolytes. Materials and Methods: Titanium was coupled with gold (Ti/Au) and nickel-chromium (Ti/Ni-Cr). For each couple, 9 surface area ratios between titanium and gold or nickel-chromium were prepared. The electrolytes used were 1% lactic acid, tryptic soy broth media, and Streptococcus mutans culture supernatant. The corrosion polarization curves were obtained, and average values of corrosion potential and corrosion current density were calculated. Results: Both Ti/Au and Ti/Ni-Cr were affected by surface area ratios and different electrolytes, showing the least corrosion rate when the ratio was 1:1 and when the lactic acid was used as an electrolyte. Conclusions: The greater the difference in surface area between titanium and restorative materials, the more corrosive behavior the materials show. The existence of bacteria such as S mutans may aggravate corrosive behavior between different metals. Int J Prosthodont 2008;21:433–436.