Alguersuari has already impressed the team at a young age
Red Bull and Toro Rosso are changing their reserve driver for the rest of the Formula 1 season.
Reigning British Formula 3 series champion Jaime Alguersuari replaces Brendon Hartley, who will continue racing in European F3.
Alguersuari, who is 19, will deputise if either team's first-choice drivers is unable to race.
The Spaniard's first race as reserve driver will be the German Grand Prix at the Nurburgring on 12 July.
Red Bull will be keen to keep up their momentum from the most recent race, the British Grand Prix at Silverstone, where Sebastian Vettel and Mark Webber finished first and second, helping the team consolidate second place in the constructors' championship.
Vettel and Webber lie third and fourth in the drivers' championship behind Brawn duo Jenson Button and Rubens Barrichello, while Toro Rosso drivers Sebastian Buemi and Sebastien Bourdais are 14th and 16th respectively.