US-based Zipcar bills itself as 'the world's largest car club company', allowing members to hire Minis, hybrids, BMWs or people carriers by the hour or day. The price includes petrol, congestion charge, insurance and parking.
Kaizo had been promoting the outfit's green credentials - more than 40 per cent of Zipcar members either sell their car or decide against purchasing one at all. The service is currently available in London, where it operates more than 5,000 vehicles.
Kaizo MD Rhodri Harries confirmed the split, adding that Zipcar's PR budget would be better spent on in-house comms.
Separately, Kaizo has been retained by US-based Ethernet outfit Neterion for UK PR, raising the brand's profile across Europe.