The 10th Fina world swimming championships get under way in Barcelona on Sunday, with Australia and the United States expected to dominate the medals.
Ian Thorpe won six titles two years ago in Japan
The championships, running from 13-27 July, are the biggest ever with 62 events - 40 of which will be swimming with the rest divided between diving (10), water polo (two), open water swimming (six), and synchronised swimming (four).
The main focus will be on whether the United States will reclaim their position as the world's leading swimming nation after trailing Australia by nine golds to 13 in Japan two years ago
Ian Thorpe, winner of six titles in Japan, could have a battle for his crown as top individual performer this time out with Americans Michael Phelps and Nathalie Coughlin tipped for individual honours.
Thorpe, who burst on to the international stage in 1997 as a 14-year-old, has made a number of changes which could prove costly, notably acquiring a new coach and a new programme.
The 'Thorpedo' is entered in four individual events but his chances of bettering his haul of last time have suffered a setback as the Australian men's relay team are under strength following the withdrawal of Michael Klim.
He will go head to head with the man who pipped him to the Olympic 200m freestyle gold medal, Dutch giant Pieter van den Hoogenband.
Van den Hoogenband won that battle, but it was Thorpe who cleaned up at the last World Championships in 2001, with six gold medals to the Dutchman's four silvers.
The pair will race in both the 100m and the 200m.
Sars undermines Chinese entry
Phelps fired his warning shot by breaking the world record in the 200m individual medley at the Santa Clara International, to add to his 200m fly and 400m IM records.
In the women's events, Dutch star Inge de Bruijn, who is the world record holder in the 50m and 100m freestyle and 100m butterfly, will participate in the 50m freestyle and 50m butterfly.
But the 29-year-old triple Olympic and world champion failed to qualify for the 100m freestyle, and is expected to be overshadowed by Coughlin as top individual.
The competition gets under way with diving on Sunday.
Olympic and world champions Tian Liang and Guo Jingjing lead the challenge of favourite's China, but the team have suffered lack of vital competition because of the Sars virus.
And Russian Dimitri Sautin, the world champion on the springboard and the 1996 Olympic platform champion, sent a warning to the Chinese by winning both the individual and synchronised springboard events in the Grand Prix super final in Mexico.
Another threat is likely to come form 18-year-old Canadian prodigy Alexandre Despatie, who impressed again by winning the platform in Mexico.
The Spanish men's water polo team, meanwhile, will be bidding to give the home crowd their third consecutive world title during the two weeks.