Objective: The U.S. intellectual property regulations allow for claiming the right of priority by an inventor by filing a patent in a foreign country or by filing a U.S. provisional patent. The study evaluated the provisional patent system introduced in 1994 by the Uruguay Round Agreement Act (URAA). Methods: Data on patents listed in the FDA Orange Book (OB) for new chemical entities approved between 1980 and 2007 were derived from the USPTO. Descriptive statistics were calculated for the variables included in the study. Chi-square and t-tests were used to assess differences between groups. Results: The OB listed 1452 patents, of which 9.6% claimed priority from a U.S. provisional patent and 39.5% claimed priority from a foreign priority filing. The mean time gained was 328.9±75.2 days from provisional patents and 340.8±60.3 days from foreign rights of priority. The proportion of U.S. companies that obtained a foreign or provisional right of priority increased from 27.4% prior to 1995 to 75.2% after 1995 (p<0.001). This increase was due to the use of provisional patents. A significant increase in the use of provisional patents and a significant decrease in the use of foreign right of priority also occurred in non-US companies, nevertheless, no increase in the combined use of a foreign and provisional right of priority was found for non-US companies. Conclusion: The foreign companies significantly decreased the use of foreign priority patents while increasing the use of provisional patents. The introduction of provisional patents to the existing foreign priority system resulted in a three-fold increase in the use of these systems by U.S. companies. The 1995 URAA change in the USPTO priority system has significantly influenced the frequency by which U.S. companies seek a foreign or a provisional right of priority.