Functional managers working together effectively is viewed as essential for NPD success, this integration of specialists is at the core of all best practice NPD processes. To achieve this integration, functional specialists need to communicate effectively with one another to achieve their respective task goals. This paper examines the role of two forms of interpersonal communication, formal and informal, on relationship investment and perceived relationship effectiveness. The relationships between these variables are tested in a structural model using PLS. Data was collected from 184 R&D Managers in Australia who worked on NPD projects with a Marketing Manager. This study provides empirical support for the proposition that managerial dependence still matters and that the human element is critical in forming effective working relationships. Whilst formal communication between managers is important in NPD projects, senior managers should also be aware of the powerful effects that informal communication has and that should also be encouraged.