During the presentation of slides with positive, negative and neutral emotional valence, EMG-reactions of three different facial muscles were recorded. The experimental group was divided into 20 extraverted and 21 introverted subjects, using the German version of the EPQ. Similar to comparable studies it turned out that the activity of the m. zygomaticus major increased presenting pictures with positive valence, whereas the m. corrugator supercilii activity increased during the presentation of pictures with negative valence. However, introverts and extraverts did not differ in their average activity of the m. corrugator and the m. zygomaticus major. Introverts showed a stronger m. depressor anguli oris reaction than extraverts. Since this muscle is used to draw down the cheeks, thereby acting against smiling, normally accompanied by an elevation of the cheeks, we hypothesize that introverts actively inhibit their facial expression of positive emotions.