White Plains - The Williams sisters and teenage Australian Open semi-finalist Madison Keys have been chosen for the United States as it seeks to return to the top group in the Fed Cup.
US captain Mary Joe Fernandez announced on Wednesday that 18-time major champion Serena Williams and seven-time Grand Slam winner Venus Williams will join Keys and 30th-ranked Varvara Lepchenko on the team that faces Argentina in Buenos Aires on February 7-8.
The 19-year-old Keys upset Venus in the Australian Open to reach her first major semi-final, where she will face top-ranked Serena.
The Americans have fallen out of the Fed Cup's World Group for just the second time since the current format was introduced in 1995.
They must beat Argentina then win another series in April to return to the top group next year.
Serena Williams last played in the Fed Cup in 2013, the previous time the US needed to win to get back into the World Group.
Former top-ranked junior Taylor Townsend will also join the team in Buenos Aires as a practice partner.
Argentina's top player is No 124 Paula Ormaechea.