This paper examines the effects of five non-coercive influence tactics (rational persuasion, consultation, collaboration, ingratiation, and inspirational appeals) on interpersonal conflict and perceived relationship effectiveness. The context of this research is working relationships between Marketing Managers and Sales Managers during NPD projects. The results suggest that the most useful influence tactic for managers during NPD is rational persuasion. This is consistent with the view that NPD projects are information processing sub-systems within the firm, aimed at reducing uncertainty. In addition, not all of the influence tactics have positive outcomes, as two of these tactics (ingratiation and inspirational appeals) appear to increase rather than reduce conflict.