Can't find the title of this movie - help!

Sorry in advance, I know this isn't much to go on but....

I'm trying to identify a movie I vaguely remember from when I was a kid - I *think* from the '90s (but possibly older, and I just *saw* it in the '90s...) and it's driving me nuts. I don't remember a whole lot about it, but I seem to remember it was pretty much a B movie, maybe even made for TV. It's a Sci-fi post-apocalyptic film where a group of people find another group and figure out they are immortal. Then they figure out they can gain this immortality, but the only way to do it is to have sex with these immortals. The catch is, there's a 50/50 chance that in doing so you would blow up.

Sounds like a real quality piece of cinema, huh? lol Anyway, if this rings a bell with *anyone* I'd be grateful to solve this mystery and get it out of my head. :P

Thanks in advance!

Sounds 'vaguely' like Teenage Caveman (the 2002 Larry Clark) version, and I'm using 'vaguely' in the loosest way possible. I don't think anyone blows up from all the sex, but theres plenty of deaths.

Hmmm... yeah, this definitely predates that one.

Possibly Zardoz (1974), but more likely a B movie inspired by it. Zardoz is set in a post-apocalyptic 2293 A.D. There are two groups of people, one of which is immortal. Sex with the immortals is a plot device. However, it does not lead to anyone dying... at least not directly.