CBS has ordered the eighth and ninth installments of its reality challenge series “Amazing Race” for airdates in the 2005-06 season.

In a format twist, the eighth installment of “Race” will feature all-family teams, which will be expanded to four members from two. The show will define “family” in a number of ways, from the traditional nuclear family to blended families and teams that can include all siblings, multigenerational relatives and in-laws. Children older than 12 will also be able to participate. The teams will follow the show’s traditional premise, which requires them to travel around the world in a quest for a $1 million prize.

The ninth installment will return to the show’s traditional casting format, in which team members must have a prior relationship, but don’t have to be related.

The seventh installment of “Race” premieres with a two-hour episode Tuesday, March 1 at 9 p.m. (ET). The latest installment features “Survivor: All Stars” winner Amber Brkich and her runner-up fianc%E9; Rob Mariano, as well as a Gulf War veteran who was a prisoner of war and his girlfriend, a former Miss South Carolina.

“Amazing Race” is produced by Bruckheimer Television and Earthview Inc. in association with Touchstone Television and Amazing Race Productions.