Males outperform females in the Mental Rotation Test (MRT) for biological, strategic and cultural reasons. The present research tested a motivational explanation with the hypothesis that females could do better when induced to have positive beliefs and expectations. All-female and all-male samples were divided into six groups, each having listened to different instructions: 1. men are better than women at this task; 2. women are better than men; 3. control instructions with no gender reference. Each group was further allocated to either the easy or the difficult task expectations condition. Experimental manipulation affected performance differently in relation to gender. Women's performance was affected by positive instructions about gender. Men were affected by instructions about the task difficulty. Women improved performance and reached men's scores in the MRT when they were led to believe they were better than men. (Contains 2 figures and 1 table.)