The pack arrives in a silver envelope with the words "be prepared" on the front. Inside is a laminate 16-page brochure containing pictures of the car from different angles alongside phrases such as "Need a moment?" and "How are you feeling?"
The final page shows BMW's performance centre, with the line "Ready to take it further?" and invites recipients to request a test drive and enter a competition to win a day driving the Z4 at the track.
The pack is being sent out to 35,000 men and women aged between 30 and 45, including drivers of rival cars such as the Porsche Boxster, Mercedes SLK and Audi TT.
Richard Downes, the customer marketing manager at BMW, added: "The Z4 doesn't really need a hard-sell, and this creative lets the car do the talking."
The car launched in June 2003 with an above-the-line press campaign through WCRS. The ad, called "speechless", showed a shot of the car with exclamation marks after it and no copy.
Alistair Bryan, an account director at AIS, said: "Direct mail often falls into the trap of drowning the product in copy. The Z4 speaks for itself, and we have taken advantage of its charisma to extend the above-the-line treatment - 'speechless' - into this execution."
The campaign was art directed by Chris Lapham and written by Debs James.