Price trends before and after patent expiration were analyzed by both price indices and fixed and random effects of regression analysis. The Fisher price index for the total market increased annually at an average rate of 7.9% during the patent protection period but declined by an average rate of 6.8% each year afterwards. For originators, the Fisher price index annually increased by 9.1% before patent expiration and by 6.0% afterwards. The rates of price change of the originator before and after patent expiration are not statistically different from each other. The price index for multiple-source drugs decreased annually by about 20% after market entry. The price decreases of multiple-source drugs are statistically different from zero.