Joining Prado and Valenzuela in the hall's 2008 class are trainer Carl Nafzger and thoroughbreds Manila, Inside Information and Ancient Title. They will be formally inducted in ceremonies Aug. 4.
Prado has added 64 wins this year to the more than 6,000 victories in his career. His career total includes wins in the 2002 and 2004 Belmont Stakes. He's won more than $202 million in purses.
Valenzuela ended a 29-year career in 1980 after winning 2,545 races and more than $20 million. He twice, in 1958 and 1968, won the Kentucky Derby and Preakness Stakes the same year.
Nafzger trained Kentucky Derby winners Unbridled (1990) and Street Sense (2007) and has more than 1,200 wins to his credit.
Manila won 12 of 18 lifetime starts, including the 1986 Breeders' Cup Turf. Inside Information won 14 times in 17 races and was the victor in the 1995 Breeders' Cup Distaff. Ancient Title had 20 stakes titles among its 24 wins and was 10th in all-time earnings when retired in 1978.