Juan Jose Haedo, 30, became the first Argentine to win a stage on the Grand Tour when he claimed victory in stage 16 of the Vuelta a Espana this year.
Lucas Sebastian, 28, joined the team last year but has struggled in 2011 after being hit by a motorbike during the Paris-Nice event.
"We have every reason to believe that the Haedo brothers will add victories to our palmares next year. At the same time both JJ and Lucas are great guys to work with and they fit well on the team," said team owner Bjarne Riis.
"JJ has proved he is a strong sprinter numerous times and added two big wins to his total this year. I truly believe there is more to come from him.
"Lucas has had a really unlucky season that was affected and pretty much ruined by his crash in Paris-Nice. So I think he deserved another chance to prove his ability to win races himself and to be a lead out rider for his team-mates."
Juan Jose added: "I have had five great years with this team, and I'm happy to stay here for another season and keep developing as a rider. Now I really look forward to the coming season to try to win some big races and help my team-mates to do so.
"That's the thing with this team, we have a really nice rider group, and being part of this team and at the same time being able to race with my brother just makes it even more special."