The fear of underperforming owing to stereotype threat affects women's performance in tasks such as mathematics, chess, and spatial reasoning. The present research considered mental rotation and explored effects on performance and on regulatory focus of instructions pointing to different explanations for gender differences. Two hundred and one participants were asked to perform the Mental Rotation Test (MRT) and were told that men perform better than women. Then they were divided into four sub-groups and provided with no additional information (control condition) or one of three explanations: (a) genetic factors, (b) widely-held stereotype, or (c) time limit. A decrease in performance was predicted for the genetic instruction and an increase for the two alternative explanations based on externalizing. Results showed that both women and men are harmed by the genetic explanation and relieved by both the stereotype and the time limit explanations. Explanations stressing genetics and time limit as factors affecting performance favor prevention focus. (Contains 2 tables.)