Wilhelm Karmann GmbH showed a convertible study based on the Mercedes-Benz C-class Sports Coupe.
The German niche assembler works closely with Mercedes-Benz.
It has produced over 66,000 CLK convertibles and more than 9,000 CLK coupes for Mercedes-Benz since 1997.
Karmann, based in Osnabruck, Germany, also manufactures the body-in-white for the Mercedes-Benz SLK.
Karmann showed the concept to demonstrate its technical and design capability, said Chairman Rainer Thieme.
Mercedes-Benz engineers worked with Karmann on the C-class Sports Coupe project, said Thieme.
The four-seat concept involved reinforcement of the A-pillar, sills and floor as well as the installation of a soft-top operated by electrohydraulics.
Karmann did not say if the concept would be produced. The prototype was not ready for production.
Karmann plans to present a second concept car later in the year, Thieme said.
Karmann's production of complete vehicles fell from 64,290 in 1999 to 54,516 in 2000, mostly because production of the Golf A3 Variant ended.
After Mercedes-Benz, the company's most important complete vehicle contract is for the Volkswagen Golf convertible. Karmann also assembles Renault's Megane convertible.
Karmann employed 7,600 worldwide in 2000.