The launch of the new Big Brother: Celebrity Hijack attracted less than half the audience of last year's regular star name format.
Overnight estimates showed 3.5m viewers watched the reality programme, compared with 7.3m who tuned into the first in for the first night in 2007.
Nearly two million people switched off when the show ended on Channel 4 and continued on digital station E4.
Celebrity Hijack sees stars act as Big Brother to a house of "unknowns".
The show was beaten in the ratings by BBC One drama George Gently which was watched by 4.9 million viewers and ITV1 drama Cold Blood, seen by 3.7 million.
But Big Brother producers will be pleased that more than one million people made the leap to E4 to watch the last thirty minutes of the live launch after the Channel 4 broadcast ended at 2200 GMT.
The new series sees celebrities setting tasks, inventing rules and talking to contestants in the diary room.
The 12 housemates, who each have a "talent", include an Olympic boxing hopeful, a classical musician and a brother-and-sister circus duo.
Little Britain star Matt Lucas was the first celebrity to set the rules during the live launch, which saw him order Scottish Youth Parliament chairman John Loughton to obey his every word.
The change in format follows the furore surrounding 2007's Celebrity Big Brother, in which Bollywood actress Shilpa Shetty was the victim of alleged racist bullying by fellow contestants Jade Goody, model Danielle Lloyd and singer Jo O'Meara.
Apart from the launch show, this year's show will not be screened on Channel 4, with nightly updates moving to E4.
Loughton is the new favourite to win the show and its £50,000 prize, with his odds slashed from 8/1 to 2/1.