This study tests four hypotheses derived from the Leader Interpersonal Influence Model, which examines leaders' ability to adapt communicator styles that enhance problem-solving effectiveness in small groups. University students participated as leaders in problem- solving groups made up of confederates. The findings indicate that the two primary dimensions of leaders' communicator style are dominance and supportiveness. Addition ally, the results show that effective leaders displayed a wider repertoire of communicator styles than ineffective leaders. Also, within an experimental situation that demands strong direction, dominance was highly correlated with effectiveness for directive leaders, and both dominance and supportiveness were highly correlated with effective ness for participative leaders. Lastly, the findings reveal that leaders' relational com munication must exceed a minimal threshold before obtaining desired responses from group members. Implications for management are outlined and suggestions are made that future research should examine leaders' communicator styles in other decision-making contexts. © 1989, Sage Publications. All rights reserved.