After you have beaten the 3th gymleader you can get the "squirtle bootle"(or somthing like that) in the flower house up to the right in Goldenrood city. Then you can water the sudowoodo with it, and he will get out of the way for you to go upp to the next city. It is here the 4th gym is.
In Gold the fourth gym Leader is Morty. Morty specializes in Ghost type pokemon, and his gym is located in Ecruteak city.
The fourth gym leader is Erika, the Grass trainer.
The fourth gym leader is Flannery.
The fourth gym at Pokemon fire red is grass type gym
The fourth gym belongs to Morty in Ecruteak city. He's a ghost type gym leader. It is located north of Goldenrod city
just beat the fourth gym leader
The fifth gym leader in Pokemon platinum is crasher wake but you get the fourth badge.
The fourth gym leader hates ghost type pokemon. ex:Gastly
the fourth gym its a fire gym
The fourth gym leader is Maylene in Veilstone City, a fighting type gym leader.
The fourth gym is in Ecruteak City. It is a ghost type gym and the leader is named Morty.
The fourth gym leader in Pokemon Soul Silver is in Ecruteak City.