I remember seeing Mr. Sardonicus, a 1961 horror film directed by William Castle, on late-night tv when I was a younger teen, but I've never seen it available on tape or dvd. It is available from 3rd party dealers through amazon.com, but I've never seen it in a local store.
The scene I remember best is the one with the dogs which had been used in the experiments.
Embedding is disabled at youtube, but the film can be watched there in 9 parts: [5/23/2010: it's gone now, even in that pitiful state]
WTF Film says, "one of the better films in Castle’s filmography, especially for people with an interest in Gothic horror beyond the initial Universal wave, Corman and Bava."