Previous research has shown that some groups using electronic brainstorming generate more unique ideas than groups using nominal group brainstorming, while others do not. This study examined two factors through which group size may affect brainstorming performance: synergy and social loafing. Groups brainstormed using three techniques to manipulate synergy and two group sizes to manipulate social loafing. We found no social loafing effects. There were significant differences in synergy, but not the ones we had theorized. Instead, we found a time effect: nominal brainstorming groups that received no synergy from the ideas of others produced more ideas than electronic groups in the first time period and fewer ideas in the last time period. We conclude that synergy from the ideas of others is only important when groups brainstorm for longer time periods and may have a harder time generating ideas. We also conclude that electronic brainstorming groups, whether in the field or in the research laboratory, should be given at least 30 minutes to work on tasks or else they will be unlikely to develop synergy.