An excellent example of drive-in fare, "Blood Mania" is a well-shot and acted sex thriller, notable for its unusual and dominant musical and electronic sounds score. It was diverting 50 years ago and holds up well as an example of horror before gore and special effects took over and became foremost in the fans' content demands.
Story of blackmail and murder makes perfect sense, with the added attraction of all the leading characters guilty of something -no good guys here. The general soap opera approach is conducive to better character acting than usual amateurism or overacting of B-horror movies. The deliberate, placid pacing works well - a more traditional approach. The biggest surprise here is the frequent sex and nudity included, tastefully presented but abundant. Stylish erotic fantasy sequences are a highlight.
Unusual plot elements are still topical, notably the antihero doctor lead being blackmailed by a handsome young slimeball for his past history of performing abortions (picture was made three years before Roe v. Wade). Claustrophobic stagings are balanced by a fine very '60s interlude of the doc starting to romance a new character, heiress Gale in S. O. L. I. footage of a renaissance fair and then gamboling in the surf.
Rewatching this film so many decades later I was reminded how entertaining traditional storytelling was before gimmicks of all sorts (mainly SPFX) took over. More's the pity.