This study compares the microleakage of a glass ionomer cement, Ketac Fil, used without cavity conditioning, with the established intermediate restorative materials, Cavit-W, and a reinforced zinc oxide-eugenol cement, Kalzinol. Microleakage was assessed using an electrochemical technique. At the end of 30 days, the materials tested, listed in decreasing order of microleakage, were Cavit-W, Ketac Fil inserted without cavity conditioning, Kalzinol, and the control group of Ketac Fil inserted into conditioned cavities. There was no significant difference in the microleakage observed in Ketac Fil restorations inserted without cavity conditioning and Kalzinol (p = 0.450), while the differences between the other groups were highly significant (p less than 0.001).