The aim of this study was to contribute to the research of psychological determinants of entrepreneurship by examining the need for achievement and entrepreneurial alertness. Both explicit and implicit measures were used to assess the need for achievement. Participants were 305 students and working people in the Republic of Croatia. They completed multiple tests, including the adaptation of the Conditional Reasoning Test (CRT-Ach) as the implicit measure of need for achievement, the explicit need for achievement scale taken from The Unified Motive Scales (UMS), the Entrepreneurial Alertness Scale and Entrepreneurial Intentions Scale. The difference between the average results of entrepreneurial and non-entrepreneurial people on the Entrepreneurial Alertness Scale indicates that entrepreneurs and proactive students are better than the rest of the population at noticing business opportunities in their environment. The difference between the average results on the UMS indicates that proactive students are characterized by stronger explicit need for achievement, while the CRT-Ach does not appear to be an adequate measure of recognizing the entrepreneurial individuals in the population. In summary, the results on the UMS correlate positively with the results on the Entrepreneurial Alertness scale and its subscales, while that was not the case for the CRT-Ach. To better understand these findings, it is necessary to expand future research by including other variables which proved to be essential determinants of entrepreneurship, like entrepreneurial self-efficacy, need for autonomy and risk-taking propensity.