The recent research on leadership has been activated under the name of the Contingency Theory. The Contingency theory does not seek all-purpose leadership applicable under any circumstances, but rather searches for related to the nature of the organization. Fielder presented a theory of leadership effectiveness which takes account of the leader's personality as well as situational factors in the leadership situation. He emphasizes that the same type of leadership style of leadership behavior will not be suitable for all situations. This theory one leadership style or another will be more conducive to group effectiveness. Fielder has considered the effects of stress on leader behavior and group performance. In general, he found (1) that low-stress conditions tend to require relatively managing, controlling leaders, while situations of moderate or interpersonal stress tend to require permissive, considerate leaders and that task-oriented leaders perform better in highly stressful conditions ; (2) that leader intelligence correlates with group performance primarily under low stress conditions or under conditions which are free of anxiety for the leader, while group member intelligence contributes to group performance under high-stress conditions and those which are anxiety-arousing for the leaders; (3) finally, that total group performance does not appear to strongly affected by the range of stress present in the laboratory studies which were discussed here.