Description: Research on professional expertise theoretically indicates intuition as a crucial component of professional expertise (Eraut, 2000). This study focuses on intuition in the domain of investment. Subjects of different levels of expertise are compared in their forecasts on stock markets. The purpose is to investigate the accuracy of intuitive and rational forecasts. Methodology: Intuition means the domain-specific capability to come to an appropriate decision without deliberately balancing various alternatives and without reflecting on a task (Myers, 2002). Intuition makes use of knowledge-resources persons developed through their career but are not necessarily aware of. This gives experts advantage over persons who do not act intuitively (Hogarth, 2001).It has been proposed that two parallel systems exist for making decisions: A rationale one and an intuitive one. The rational system demands attention, awareness, and time, whereas the intuitive system stays beyond the level of consciousness and allows quick and appropriate responses. Thus intuition can hardly be verbalized and has to be assessed indirectly.A typical task in the domain of investment is to forecast developments on the stock market. Even if it is a daily task of investment professionals, it can be done in different ways, depending on time pressure and on the need to rationally defend one's decisions. In consequence, there is ample variance of individual experiences and of the degree of conscious assumptions. Thus, forecasting tasks are appropriate to investigate intuition (Klein, 2003).Research Questions(1) Do intuitive forecasts and rationally justified forecasts differ in accuracy and quality?(2) Are experts' intuitive forecasts better than novices'?MeasuresIn an online questionnaire subjects forecasted the development of six important German stock market values nine months in advance. They had to put the expected number in an input mask. For intuitive forecasts, answering time was limited to 15 seconds, which is considerable time pressure. For rationally justified forecasts no time limit was set, and subjects explicitly had to write down rational justifications of the decision. A basic assumption of this study is that if subjects are forced to rationally justify forecasts, then intuitive ideas are suppressed. Under time pressure however, intuitive forecasts are forced. The accuracy of the forecasts was measured referring to the effective stock prices on December 2005. In order to control for effects of sex, age, and reaction time, these variables were measured in a second online questionnaire. Conclusions: The control variables did not show any significant influence on the results. Concerning the forecasts, the following results emerged:(1) Intuitive forecasts were closer to the effective stock exchange prices than rational ones. (T=-2.99, df=31, p=.04)(2) Experts and novices did not significantly differ in accuracy of forecasts (Main effect "level of expertise": F(1,1)=0.196, p=.66)Finding 1 indicates that intuition can influence the accuracy of stock forecasts. Thus, it can be seen as a component of professional expertise in the domain of investment. However, result 2 shows that also novices can reach experts' accuracy. A repetition study starting on March 2006 should investigate if this is an effect of chance.