It makes Howard Karp angry to think about the jeering, the laughter and the catcalls of the Poles, as he and 1,500 other Jewish teens linked arms and walked from Auschwitz to Birkenau on the March of the Living last month. His voice softens, though, as he recalls the reaction of one boy in particular.

"He was probably my age, 18 or so. I made eye contact with him," Karp said of the young man watching him through the window of a passing bus. "He gave me such an approving look, like we were keeping the Jewish faith alive.

"I don't know if he was Jewish or what. All I know is I was so proud to be one of those 1,500 wearing the blue march jacket with the Star of David on the back."

Usually the March of the Living is held every two years, and attracts about 6,000 teens. However, organizers decided to hold the event during an off year to commemorate the 50th anniversary of the end of World War II in Europe. As a result, the last-minute effort attracted only 1,500. Karp, an 18-year-old San Mateo resident, was among the handful of Bay Area teens walking the three-mile trek.

Karp, a member of Peninsula Temple Beth El, toured Poland for nearly a week. During that time, he traced the footsteps of Jewish concentration camp prisoners before heading off to Israel.

Like many marchers who have participated since 1988, Karp was "blown away.

"People always say you'll come back a changed person. But I didn't know what they meant. I've been back two weeks now and I still don't know how I'm a changed person," he said.

"But I know you can't go to Poland and see Auschwitz, see Birkenau, see the ashes and bone and teeth and hair and shoes and gloves and come back the same person.

"In a way I feel as close as you can to being a survivor without being one."

Jeff Stein, an 18-year-old senior at Leigh High School in San Jose, agreed.

In addition to learning more about the Holocaust and anti-Semitism, Stein discovered the hatred that "moves us as Jews, affects us all," he said.

He recalled seeing his Polish tour guide hold back tears as he followed the group on the journey.

"He has no direct link to us, but like us, he too was affected just by going," said the member of Congregation Shir Hadash in Los Gatos. "We all get the same message."

Karp and Stein, who returned to the United States May 8, think of their trip often. They also talk about it a lot — to each other, to high-school classes and to local synagogues.

Stein is haunted by the smokestacks he saw rising above what remains of the two Nazi death camps.

"Those first chimneys, they were only the kitchens. The crematoriums were much bigger," he said.

"You never see chimneys the same again."

Karp remembers lifting up the barbed wire fence surrounding Auschwitz and crawling under it, his face pressed against the wet earth. It was his way of trying to understand how the prisoners felt, he said.

"I wanted to get dirty, to challenge myself," he said. "I knew I might get cut. I wanted to risk something dangerous for the hardships they went through."

And then there was the joy of flying into Israel for the second time in his life, and celebrating Yom Ha'atzmaut in the Holy Land.

"When we arrived in Jerusalem, I felt like I was home," he said.

The strong feelings expressed by Karp and Stein are not unusual for teens who go on the march.

"This is definitely one of the most transforming experiences for participants and their families," said Mickey Naggar Bourne, coordinator of Israel programs for the S.F.-based Bureau of Jewish Education, the local coordinating agency for the March of the Living.

Although the experience can be rewarding, it's not for everyone, she added.

"This is a very self-selecting program. The kid who comes to us is strong already," she said.

The teens may be more secure than others, but they remain vulnerable to the powerful images and symbols of both Poland and Israel.

Dan Rochelle visited Israel two years ago with his confirmation class at San Francisco's Congregation Emanu-El. "It was fun, but this time it was different," he said. "I fell in love with Israel."

Yet the 17-year-old Foster City resident is disturbed by his experiences in Poland.

"I'm still depressed from what I saw," he said. "It's hard for me to look at my pictures. I don't want to forget the trip. I see flashes of moments there. I miss the people. It's a special bond between us."