"ARE YOU READY?" asks Dr. Rohlen.
"No problem," I boast. "I've skinny-dipped in the Arctic Ocean."
Next to me is a square bucket bubbling with 32-degree water, ice cubes bouncing on the surface, a fish-tank aerator circulating the mix. Dr. Brooks Rohlen, a fit 38-year-old resident at Stanford University's Human Pain Research Laboratory, reaches for a stopwatch. Martha Tingle shifts the bucket a little closer. A tall, shy 52-year-old with cappuccino skin, she's a registered nurse and the lab's manager. Its founder, slender Swiss anesthesiologist Martin Angst, dressed in a black T-shirt and dark jeans, looks on quietly, as he will most of the day.

"Place your palm on the bottom of the tub," Dr. Rohlen says, smiling a little too brightly for someone about to dunk my hand into a vat of ice water. "Keep your hand there until it is no longer tolerable." His teeth glow as white as his lab coat; his hobbies—coaching the Squaw Valley freestyle-skiing team and running a charity that helps people establish memorial funds—would be full-time jobs for most people; and his boundless energy scored him a $40,000 research award on top of his anesthesiology residency. He's driven, kind, and funny, though sometimes it's difficult to tell which. Before I arrived at the Pain Lab, he said (and I quote), "We'll have you wetting your pants and calling your mom, but we'll send you home with a free sweatshirt."

Looking around, I'm beginning to wonder if he wasn't joking. The Pain Lab lies in the far northwestern corner of Stanford's sprawling Palo Alto, California, campus, tucked away on the lonely fourth floor of the medical center. Every surface has been scrubbed, scoured, and disinfected; all olfactory evidence of the living has been erased. No windows allow anyone to look out or observe the goings-on behind the heavy locked door. I'm sprawled out on the lab's single full-length chair, spotlighted under two enormous reflector lamps. Laptops perch at each armrest, connected to a network of tubes and wires of indeterminate function. Nearby are racks of needles, rolling metal carts holding a ten-barrel Saalmann Multitester for creating sunburns, and a perfusion pump, which can inject subjects with enough narcotics in ten seconds to stop their breathing. There's a black gun safe full of drugs and, behind the chair, an honest-to-God shock-therapy machine that Dr. Rohlen assures me is used chiefly by a Russian associate named Vladimir. The Pain Lab is clearly either a sort of brilliant skunk works or the new leader in barbaric testing.

The ice bath is designed to determine the most important measure: my pain tolerance, or how much nerve-ending overstimulation I can endure. I assume I'm tough as toenails. I've swum beside ice floes, slept in snow caves, skied through frostbite, and scaled a snowy 15,000-foot pass with plastic bags on my feet (long story). I'm no Delta Force candidate, but I'm pretty confident I'm not constitutionally a sissy.

At Dr. Rohlen's nod, I plunge my hand into the water. At first, I feel nothing; then, after a few seconds, X-Acto knives begin lightly slicing the tendons of my wrist, scoring deeper and more sharply the higher they cut, and my cuticles and joints begin to throb. Then a thousand pins prick the back of my hand as all the discomfort crescendos. I fling my hand out.

"Oooooh," I groan.

Surely minutes have passed. Rohlen looks at his watch. I lasted precisely 11.49 seconds (as ex-girlfriends will confirm). Relative to most test subjects, I came up grossly short: eight seconds under the average.

I'm not sure why I stomached so little. Maybe it was because I freaked out and thought the bath was full of hydrochloric acid. Maybe it was because as soon as Nurse Tingle grazed my wrist I wanted to blurt, "It hurts! Everything hurts." Or maybe it was because of one of the main scientific mysteries the lab is unpacking: why one person's agony is a far cry from another's.

"Not even close," Dr. Rohlen declares, noting that some people keep their hand plunged for up to a minute. Translation: "You're a pantywaist."