There will be an additional 75 places in the 2010 Routeburn Classic - this year being held two weeks earlier in the hopes competitors will not have to contend with snowy conditions.
Race director Evan McWhirter, of Good Time Events Ltd, said the 225 available spots were snapped up within 30 minutes of going online last year and more than 100 people were on a waiting list for the event.
Now in its seventh year, the race will attract runners to The Divide, near Milford Sound, for the 8am start gun on April 24 and will finish near Glenorchy.
The fastest athletes are expected to cross the finish line in just under three hours.
This year a total of 350 places will be up for grabs when registrations open online at 7am on Monday.
