Sasuke Retrieval Arc

After returning with Tsunade (in the anime, after returning from the mission in the Land of Tea), Sasuke began to fall into the corruption set in place for him by Orochimaru. He began lashing out at Sakura and Naruto, not as team-mates but as enemies, eventually defecting from Konoha in order to seek out Orochimaru for power. Under the escort of Orochimaru's Sound Four, Sasuke left to join Orochimaru, and Naruto joined a retrieval team that would bring him back; he also made a promise to Sakura that he will bring Sasuke back at all cost. While the other members of the team dealt with the Sound Four, Naruto finally engaged in a fight with the Sound Four's fifth member, Kimimaro. However, he was not able to beat him even with Nine Tails-enhanced shadow clones. When Naruto was about to be killed, he was saved by Rock Lee, who told him to continue the pursuit of Sasuke while he fought Kimimaro.

Sasuke and Naruto face off.

Naruto finally caught up with Sasuke in a place called Valley of the End, very near the border of the Land of Fire and the Land of Sound, and fought Sasuke. With Sasuke determined that he would kill Naruto in his quest for power, Naruto decided he would have to take the battle seriously if he was to bring Sasuke back. When Sasuke's drive to kill proved greater than Naruto's resolve of friendship in a 'fair' fight, Naruto tapped into the Nine-Tails' chakra to level the playing field, allowing him to batter around Sasuke. Sasuke, pushed to his limits, managed to develop the mature Sharingan, greatly overpowering Naruto. When Naruto, even with the Nine-Tails' chakra, was defeated, he tapped into the chakra even more, and a red aura of the Nine-Tails' chakra, in the shape of a fox, surrounded him. Sasuke then drew on the power of the second stage of his cursed seal to properly compete with Naruto.

Naruto clashing with Sasuke.

The two had one final clash, Naruto with his Rasengan (enhanced by the Nine-Tails' chakra) and Sasuke with his Chidori (empowered by the cursed seal). Upon contact, a giant, black energy dome formed and surrounded them. In the dome, Sasuke struck Naruto in the stomach, while Naruto scratched Sasuke's headband, proving the latter's earlier taunt of the subject wrong. Sasuke won the fight, but after staring at the unconscious Naruto, he couldn't bring himself to kill his best friend, so he simply continued on his way to Orochimaru.

Kakashi and Pakkun didn't come in time to get Sasuke, and left with Naruto. In the hospital, Naruto vowed to Sakura that he would someday bring Sasuke home. Soon after, Jiraiya arrived suddenly, telling Naruto to train with him for three years prior. He also told him to give up on Sasuke, as he is no different from Orochimaru. Naruto accepts training with Jiraiya, but rejects to giving up Sasuke. In the manga, right after this, Naruto departs, but in the anime, he stays for a while, doing numerous filler arc missions.