Interesting comments from Reggie above, as ever. He knows his blues history better than I do and well enough to know that "Rolling and Tumbling" (or whatever Dylan calls his version) was recorded by Robert Johnson as "If I had Possession Over Judgement Day". Big Bill Broonzy's "Worrying You Off My Mind" used the tune of Robert Johnson's "Come On In My Kitchen". I am sure Max and Bobert et al could all swamp us with other examples. Consciously and subconsciously this has been going on for as long as blues and folk music itself. I think it has just become more of an issue since publishers have been able to generate and earn vast profits from copyrighting music. In Dylan's blues songs, as in some of his early sounding "folkie" stuff - as in the examples given earlier in this thread - I think he has leaned more heavily on existing melodies. No one did that more than Woody Guthrie and his legacy as an original is beyond reproach. It would be very unfair though to accuse Dylan of not being capable of creating original melodies. I think he just uses the tunes, which he likes best at the time, whether they happen to originate in his own imagination or not.