The research questions of this study are the following: To what degree can results such as those of Thayer and colleagues (1978a, 1985, 1986, 1988) concerning diurnal variation and differences between diurnal types, obtained for energetic and tense arousal, be (1) replicated, (2) extended to elation and pleasantness, and (3) generalized to positive and negative affect? With regard to energetic arousal, all results were in line with those of Thayer and colleagues. However, regarding tense arousal, there was an unexpected main effect for time of day. For energetic arousal, elation, pleasantness, positive affect, and negative affect, there was (a) a significant main eflect for time of day, (b) a quadratic trend for diurnal variation, and (c) a significant Diurnal Type × Time of Day interaction, There were no significant sex differences in diurnal variation. Two final hypothetical statements are made about the diurnal variation and differences between diurnal types with regard to state scales: (a) the diurnal variation of a state scale cannot be described with a quadratic function if that scale is completely unrelated to energetic arousal; and (b) the characteristic differences between morning types and evening types, especially when measured in the morning and in the evening, will not manifest themselves on a state scale if that scale is entirely unrelated to energetic arousal. Finally, the possible usefulness of the results of this study for practical applications and the development of theories are discussed.