Ledger, who died from an accidental overdose of prescription drugs in January, was urged to seek help by crew on The Dark Knight after he reportedly became too involved in his character.
Bale rubbished the speculation in an interview with Total Film, saying: "It's not for me to tell anybody or to pretend to have insights beyond what I absolutely know, but my instincts are that the idea Heath was disturbed by playing The Joker is ridiculous.
"Heath was somebody who, like myself, acted for that immersion in a character. It's not an unusual thing.
"And from working with him and knowing him, I don't think that was unusual for him at all."