The effects of metrifonate (3, 10 and 30 mg/kg, p.o.) on the working and reference memory performance of the rat were assessed in a spatial cone field task. The highest dose of metrifonate (30 mg/kg) improved the working memory performance, whereas none of the doses affected the reference memory performance. Other parameters of spatial discrimination performance were not affected by metrifonate treatment. The present results suggest that metrifonate has cognition-enhancing properties which are likely to be related to aspects of (spatial) working memory.