MIAMI -- Ask any five people about Key lime pie and they will agree on one thing only -- it should never ever be green.

''Honey,'' said the slight waitress with weather-beaten skin at a little dive called the Crack'd Conch (where the choices for dessert were a slice of Doris's Key lime pie or the whole pie), ''if it's green, man made it green. One more thing,'' she added as she set the pie before us, ''you're never gonna find two Key lime pies that are the same.''

No kidding.

Whipped cream topping or meringue? Slathered over the top or a dollop? To bake or not to bake? Frozen or just chilled? If limes from the Florida Keys aren't available, will Persian lime juice, key lime juice concentrate, or key limes from Mexico do? The answers include ''absolutely!'' and ''absolutely not!'' What's a Northerner to do? The solution seems obvious: Taste all the pies you can.

The essential ingredient, of course, is Key lime, a tiny ping-pong ball that yields only a few teaspoons of juice. Sold in mesh sacks, Key limes are in season in Florida from April through November (but available year round from Mexico and Central America). When they're ripe, they're yellow, rather than green, and their tart juice can almost be sweet, making them perfect for baking pies.

Residents of the Keys insist there is something special in the coral rock and soil that gives their limes an especially astringent flavor and distinct aroma. In a blind taste test there was a difference.

Most Key lime pies have a pale yellow, almost white, custard filling made with lime juice (often a mixture of both Key limes and the more common Persian limes), egg yolks and condensed milk in a graham cracker crust. Some contain grated lime rind, others are made with milk, cream cheese, vanilla ice cream, or meringue. One lady, overhearing a request for a good pie recipe, offered her low-fat version made with yogurt, lime Jell-O, and (horrors!) green food coloring. Some folks add rum or chocolate chips or use a regular sweet pie crust.

Purists will argue endlessly over the ''classic'' pie. It's not unlike the thick versus thin clam chowder debate hereabouts. At The Key Lime Tree garden and gift shop in Key Largo, clerk Judy McGraw was mulling over a question about pies when all heads turned. McGraw whispered, ''you can start a war down here by asking about Key lime pie.''

Claims of ''best'' were dropping like ripe fruit from trees. Gift shop owner John McCarthy believes the petite citrus fruit contains detoxifying elements. He says ''old conchs'' (that's Southern for ''old salts'') will come into his shop, pop the top off a bottle of key lime juice, and gulp it down to cleanse their kidneys. Besides his pies, he also uses Key lime juice to make concentrate, shampoo, body lotions, and jellies.

Most Florida restaurants and bakeries have Key lime pie on the menu. The differences are often very subtle but when faced with a cloyingly sweet pie and fake whipped cream, you notice it. Miami Herald food editor Kathleen Martin says a good Key lime pie should balance sweet and tart ''just on the tart side of the meter.'' She thinks few palates could distinguish between a pie made with common Persian limes instead of Key limes, but her own pie is made with fresh Key lime juice, rather than bottled, when the fresh fruits are available.

One of the best pies -- one that has a creamy, light filling, just the right bite of fresh lime, and a dollop of real whipped cream in a thick graham cracker crust -- is made at Joe's Stone Crab Restaurant, Miami's big popular fish house, where an entire kitchen produces about 30,000 handmade pies a year. There, the bakers use both fresh Key and Persian limes.

If you have a hankering for a slice and don't want to leave your fireside, Joe's will ship one to you for $69 (a plane ride may be cheaper). While you're at it, get a mess of crab claws, too. The Blond Giraffe in Key West (a favorite of many Miamians) will also ship a pie for about the same price. Blond Giraffe pies have a high meringue topping and will stay frozen for several months.

Or, you can just start squeezing. Making Key lime pie is easy. It takes one-half to one cup of lime juice -- about 8 to 14 Key limes -- for a pie. If you find them, or some kind relative brings you some, get a few bags. You can freeze them whole and once thawed, the juice flows easily. Or, squeeze the whole lot and freeze the juice for 2 to 3 months. Putting together your own graham cracker crust is a snap and tastes better than the prepared variety. Key lime juice concentrate makes a fine pie (try ''Real Key Lime Juice'' from www.famousflorida.com).

Let the fresh lime smell make you dream of warmer days ahead, when the trees (never the pies) turn green.

Key limes are sometimes available at Wilson Farms, 10 Pleasant St., Lexington (781-862-3900). You can order them by the case. Most Bread & Circus stores carry Key limes. Products from Key Largo's The Key Lime Tree gift shop are available at www.keylimeproducts.com. Search for Blond Giraffe pies at www.blondgiraffe.com, for Joe's Stone Crab pies at www.joesstonecrab.com.