I would like however to say that whilst I think that the Mamoulian is the superior film, March's "good side" didn't strike me as much as Tracy's, which is much more believable. On the other hand, Tracy's Hyde is definitely not in the same league as March's, which is not to say that it isn't a fine performance (in fact, it's a lot more subtle and a tad creepier at times) but March simply changes into a totally different...erm... entity or something!
But yeah, thank you so much Eclisse for bringing this title to our attention. I had some terrific fun watching this. By the way, I think Dr. Jekyll was on to an early version of amyl nitrite, wasn't he?