This is the first paper to study the impact of long‐term tariff reductions on capital spending by US manufacturers. We investigate fluctuations in investment for approximately 400 different four‐digit industries during the period 1974–2005. Our results indicate that the dismantling of tariff and quota protection has had a stimulatory effect on US manufacturing investment, despite the relatively low average tariff rate that existed at the start of our sample period. However, our findings reveal that reductions in input tariffs rather than output tariffs were the source of this effect, suggesting that better access to foreign inputs rather than increased foreign competition at the output level served as the primary stimulus for increased US manufacturing investment.