This study compared four interim endodontic filling materials for microleakage. Forty extracted premolars were prepared for first appointment endodontic therapy. Each tooth was filled with one of four materials, thermocycled, placed in basic fuchsin dye, sectioned, and photographed. Ketac-Silver showed virtually no leakage; IRM exhibited leakage ranging from minimal to the depth of the dentin; Term had leakage ranging from slight to the depth of the pulp; gutta-percha exhibited leakage in the various samples from deep dentin penetration to pulp chamber penetration. Ketac-Silver demonstrated superior sealing qualities compared to the other three materials. The gutt-percha was remarkably inferior to the other materials.