The Madrid–Barcelona air route constitutes one of the main aerial routes in the European corridor in terms of traffic demand (4.2 million passengers in 2003). To deal with such a high demand, three airline companies (Iberia, Air Europa, and Span Air) globally offer more than 60 flights per day either way. Currently, the construction of a high-speed railway line between the two cities is under way. The line is expected to come into commercial service by 2007, covering the whole of the 625 km between the cities. This article analyzes the impact that high-speed railway services have on air traffic demand. The results are then compared with real data corresponding to the Paris–London line, on the occasion of the launch of the commercial service of the high-speed Eurostar train.