Dragon Ball GT - episode 35 - 28 Jan, 1997

Again, the transformation was shown, but at the beginning of the episode this time. In his new state, Goku's powers are incredible and is now an adult again, thanks to the power of his newly-restored tail. He finds Baby, and they begin to fight. It seems like Baby still has the upper hand, but Goku reveals that he hasn't even been trying. Now on the offensive, Goku seems indestructible. Baby is no match for him. Bulma contacts Baby, saying that she's found a way to focus Blutz Waves onto him, which would turn him into a Great Ape. She hits him with this beam just before Goku releases a Kamehameha wave, and Baby transforms into a Great Ape (in Super Saiyan form). (Source: Wikipedia)