Purpose: The sealing of provisional filling material in overdenture tooth abutments during provisional rehabilitation is of primary importance to the long-term success of roots bearing gold casting copies. The aim of this in vivo study was to evaluate the microleakage of four different provisional filling materials after a period of 1 week. Materials and Methods: Five patients needing treatment with overdenture prostheses and scheduled for the extraction of at least four teeth were chosen. After performing endodontic treatment on the roots to be extracted, a standardized cavity preparation 3 mm in depth was made using a diamond bur. Each cavity was filled with one of the four provisional materials selected for the evaluation (Cavit-W, IRM Caps, Guttapercha, Fermit-N), and the interim prostheses were delivered to the patients. After 1 week, the roots were extracted and stored for 24 hours in 0.5% basic fuchsin at 37 ± 1°C for 24 hours. Subsequently, the roots were severed and observed under a stereomicroscope for microleakage evaluation. Results: The materials showed different degrees of microleakage, but none allowed dye penetration to the bottom of the cavity. IRM Caps showed the lowest mean value of dye penetration (168 µm), while Fermit-N showed the highest (1,475 µm). All materials differed from each other (P < .05). Conclusion: Within a period of 1 week, the materials provided acceptable to good sealing properties. All of the materials may be considered suitable for provisional fillings if they do not remain in the oral cavity for more than 1 week. IRM Caps gave the best results. Int J Prosthodont 2002;15:479–482.