Kyuubi Unleashed
Immediately after Yamato signals Naruto and the others out to the bridge where Orochimaru and Kabuto are waiting, Naruto's chakra begins to boil with the chakra of the Nine-Tailed Fox. Slowly, Naruto grows more tails as Orochimaru taunts him and makes him even more angry. Meanwhile, Yamato remembers Jiraiya speaking of how many tails he has seen Naruto grow. Jiraiya explains more about what happened and more about how Naruto acts when he's in his Nine-Tails form.
Aired 20/12/2007EP 40 - Kyuubi Unleashed
Naruto: Shippuden
Naruto: Shippuuden is the continuation of the original animated TV series Naruto. The story revolves around an older and slightly more matured Uzumaki Naruto and his quest to save his friend Uchiha Sasuke from the grips of the snake-like Shinobi, Orochimaru. After 2 and a half years Naruto finally returns to his village of Konoha, and sets about putting his ambitions to work, though it will not be easy, as he has amassed a few (more dangerous) enemies, in the likes of the shinobi organization; Akatsuki.
(Source: Anime News Network)