Anthony Ervin auctioned off his gold medal for winning the 50-meter freestyle at the 2000 Sydney Olympics to aid victims of the Indian Ocean tsunami.
Now, he wants another one.
"Hopefully I can make that happen in the next two swims," he said.
Ervin swam the fourth fastest time in heats for the 50 free Thursday morning and will go again in the evening, when the Aquatics Centre will also host the second head-to-head race between Michael Phelps and Ryan Lochte.
Two years after winning gold and silver in Sydney, Ervin retired from swimming at the age of 22 in 2003. The former world record holder in the 50 free went back to college and toured the world, but got back in the pool for a college assignment and came out of retirement to qualify for the event again at U.S. trials.
"It is part of the human experience to push and push what we think is possible," he said Thursday.
Trinidad & Tobago's George Richard Bovell had the fastest 50 heat, 21.77 seconds, while world record holder and reigning Olympic champion Cesar Cielo was .03 ticks slower. Cielo hasn't lost at the distance since winning gold in Beijing four years
American Cullen Jones also made the semis, coming in sixth. He and Ervin will try to bring the U.S. another sprint medal after Nathan Adrian won the men's 100 free Wednesday night.
Lochte and Phelps set themselves up for their second head-to-head race of the London Olympics after both made the final of the men's 200 individual medley.
The world record holder Lochte blew away Hungary's Laszlo Cseh by .61 seconds Wednesday night for the fastest time in the semis. But Phelps is the two-time defending champion at the distance and will be looking to become the first male swimmer to win the same Olympic race three times in a row two days after setting the all-time Olympic medal record. He was .98 seconds slower than Lochte in the semis.
It's their last head-to-head race of the games. Lochte, of course, won the first one -- the 400 IM on Saturday in the first medal race here. Phelps was fourth, the first time he finished off an Olympic medal podium since he was 15.
Americans have 18 swimming medals here so far, and they're evenly split among the men and women: 4 gold, three silver and two bronze for each.
The final of the men's 200 backstroke is also Thursday night, about 30 minutes before the 200 IM. Lochte also qualified for that race Wednesday night with the second best time in the semis behind U.S. teammate Tyler Clary.
Phelps will end his night with semis for the 100 butterfly, which he has also won in the last two Olympics. He had the second fastest time in heats in the morning behind South Africa's Chad le Clos, who beat him in the 200 fly -- Phelps' signature race.
It was the last Olympic preliminary swim for Phelps, who swears he will retire after the games.
"This is my last prelim swim ever so that was pretty fun to be able to do a pretty decent time in it," he said.
Milorad Cavic, the swimmer Phelps beat by .01 seconds in the famous Beijing 100 race, also made the semis.
American Rebecca Soni will defend her Olympic title in the women's 200-meter breaststroke after setting a world record in the semis Wednesday night and Missy Franklin will take aim at her fourth medal here in the women's 100 free.
Franklin, who will be the first American female swimmer to race in seven events at an Olympics, had the fastest heat Wednesday morning in the 200 back ahead of teammate Elizabeth Beisel and world record holder and two-time defending Olympic champion Kirsty Coventry of Zimbabwe. Franklin already won the 100 back.
Britain's Rebecca Adlington, the world record holder and 2008 gold medalist, swam the fastest heat for the women's 800 free Thursday morning. Denmark's Lotte Friis was second and Katie Ledecky of the U.S. was third.