This paper explores the effect of recent U.S. tax changes on the R&D activities of American multinational corporations. Prior to 1986, U.S. multinational firms could deduct all of their domestic R&D expenses against their U.S. income for tax purposes. After 1986, some firms could take only a partial deduction (while other multinationals continued to receive the benefits of 100% deductibility). By comparing the behavior of firms in these two situations (after 1986), it is possible to estimate the responsiveness of R&D to changes in after-tax prices. The results indicate that the price elasticity of demand for R&D lies between -1.2 and -1.6, thereby implying considerably more price sensitivity than is typically assumed to be true of R&D. Based on these results, the 1986 tax change appears to have been responsible for a reduction of between $1.4 billion and $2.2 billion in annual R&D in the United States, in return for $1.2 billion in additional annual tax revenue.