A couple of weeks ago, unsealed envelopes appeared on the sides of about half the Pentagon's 40 soda machines. They were taped in place, with a note beside each one that urged soda-buyers to drop their pop-tops inside. The tops would be sold to buy "dialysis time" for the victims of kidney disease, the notes said.

I'd been wondering when -- and in what form -- this perennial would resurface. Now I know.

A lot of people believe you can save cigarette packs and turn them in for "dialysis time." Others believe it's cigarette butts. I've even heard of some people who save the spent cartridges of ball point pens. And now, Pentagonian pop-tops.

Forget it, folks. None of these methods buys "dialysis time" for anybody. Never has. Doesn't. Never will. And that's not just me talking. The staff at the Kidney Foundation of the National Capital Area will tell you the same thing.

They'll also tell you that nothing is more demoralizing to kidney patients than to hear this rumor year after year. "Dialysis time" ain't cheap, and kidney patients would love to think there's an easy way to pay for some. Each time one of these "collectible" drives surfaces, the hopes of these patients get raised. Then they fall to earth with a great thud.

Where do the cash-for-trash rumors start? No one is sure. I've tried to trace them several times. The trail always grows cold -- as it did with the pop-tops at the Pentagon.

A Defense Department spokesman said he was "not aware of how they the envelopes came to be attached to the machines." Norma Bouras, administrative assistant for the Pentagon's Concession Committee, which supervises the soda machines, said that "no one has requested anything of this nature, and no one was authorized to put the signs up." (By the way, Norma has since ordered both the envelopes and the signs taken down).

Coke and Pepsi can't shed any light on the matter, either. Delores Colonese, an executive secretary at Pepsi, said the company "has no such program going on." Ditto at Coke, says sales manager Don Armstrong, who adds drolly that it couldn't be anything Coke and Pepsi organized jointly because "Coke and Pepsi don't do anything in conjunction with each other."

At least Don's understatement brings a chuckle. The situation as a whole does anything but.

To whoever put up the envelopes and signs at the Pentagon: I'm sure your motives were the purest. But there is absolutely no value to 25 envelopes full of pop-tops. If you want to help kidney patients, the best thing you can do is pass the hat.