Saint-Gaudens - French rider Thomas Voeckler defends the yellow jersey as Tour de France rivals set off on Saturday's 14th stage for a third consecutive day of tough climbing.
Saturday's 168.5km trek from Saint-Gaudens to Plateau de Beille is the most grueling yet in the Pyrenees.
It starts with a sharp climb up Col de Portet d'Aspet followed by two ascents up Col de la Core and Col d'Agnes, and then finishes with a huge 15.8km climb to Plateau de Beille, a famed and tortuous ascent.
Defending champion Alberto Contador needs to make time up on his Tour rivals Cadel Evans and Andy Schleck and could launch one of his trademark attacks on the uphill finish to Plateau de Beille.