This is the first episode of the fourth season, Pokémon: Johto League Champions.
This episode marks Ash's only Johto Gym loss.
Although the Goldenrod Gym specializes in Normal-type Pokémon, Whitney battles Ash using a Nidorina, a Poison-type.
This is the first episode in the dub where the first section of an episode starts followed by the opening theme, and the title card comes right after it. The original Japanese version wouldn't have a cold opening until AG146, 262 episodes later.
The dub introduces a new title card, replacing the original one used in the first three seasons.