Today, an increasing amount of main suppliers are using sub-suppliers to perform different tasks in the product development process. As a result, the knowledge needed to develop a new product is distributed among many actors. Knowledge management is a comprehensive term for providing the right piece of knowledge to the right people at the right time. This paper deals mainly with the question of how knowledge is managed in collaborative product development between main and subsuppliers (system level). The results are based on a case study with one main supplier and ten of their subsuppliers, in which the main suppler develops, assembles, and delivers a whole, complex product to the customer. The study shows that the subsuppliers' knowledge and experiences are not fully utilized in their relationship with the main supplier. Finally, some different ways of working are discussed in the paper's recommendation section, to improve the knowledge exchange between main and sub-suppliers.