(Various and sundry fly-by-night companies have released it over the years - try www.gemmvideos.com)
Ahhh... the insanity of 70's Spanish cinema. Highly underrated at times, and sometimes totally, threshold-of-pain awful. But don't let that stop you, because there are a few gems in the mix worth looking out for; many that have been buried time and time again, but seem to re-surface somehow. And you know how they do that? They rename the fucking things, over and over again just like they did with a lot of the martial arts films) and re-release them, but- if you're in Boston, anyway- you can always go to Video Oasis (All hail Dennis...HAIL!) in Cambridge, MA and have them get the real-deal version of it, so all is well.
Now, this just got released again on a comp DVD of 4 movies called "Pray for Death", and what a bodacious ride this one is. Two girls who are friends in a convent (Yes, we know where this is going now, don't we?) - one is the sweet virginal one, the other one has the black robe and piercing eyes, with that look of Pagan-rific gleam on her face, (Oohh, I'm the naughty one folks, evil woman...look out.) They run off into the woods, and encounter a mysterious hunchback (I'm not an animal... I'm an extra in a sleazy Spanish Nun yarn), and when they return to the convent, the sweet virginal one goes possession lane, and starts sprouting all sorts of stuff that would make even Cradle of Filth blush, leading to all sorts of maniacal 70's exploitation
mayhem - and folks, its not pretty. 
Well, that all depends on your point of view.
Possession, buckets of nudity, nuns flogging themselves, lesbianism, a scientist who does not believe in the unknown, but can't find a reason for what's going on. Well, duh. He's kinda like that doctor in Zombie- "There has to a rational explanation for this!" There's also raining blood, a head nun who sweats blood (no witty banter from me on that one.), and enough screaming and whacked-out, red-hued, tripped-out lunacy to choke a hundred faceless drama queens leaving a dance club. Unreal, to say the least. It is available in England on DVD, and you can find versions of it online if you look hard enough. Go get it. You won't be disappointed. - Greg Dellaria