In order to investigate the subsystems underlying the recognition of facial expressions, two experiments were conducted using the prolonged viewing method. Pictures of female faces were presented in the following 6 categories, 'happiness', 'sadness', 'surprise', 'anger', 'disgust' and 'neutral'. In Experiment 1,Ss orally judged the expression of a test face following either 1 second or 25 seconds of viewing of an upright adaptation faces. The delays produced by the prolonged viewing were calculated by comparing the reaction times under both viewing time conditions. Significant delays occurred when the adaptation faces had high absolute values on the first component (derived from a principal component analysis) which corresponded to 'pleasantness" ('happiness'-'disgust'). In contrast, adaptation faces which had the high absolute values only on the second component ('sadness'-'surprise') produced no effects of prolonged viewing. In Experiment 2,such effects were found to disappear if the Ss viewed inverted adaptation faces. It was suggested that there are at least two subsystems involved in recognizing expressions of upright faces.