The present work deals with the internal and external influences on emotional experience at work. Emotional experience was operationalized by two bipolar dimensions of affect, positive affect (PA, activation-deactivation) and negative affect (NA, good-bad mood), in a modified version of Positive Affect Negative Affect Model developed by Watson and Tellegen (1985). Different work characteristics (workload, control, social support) were used as external factors and their influence on PA and NA was measured. Moreover, the influence of circadian rhythm as internal factor was analyzed by the experienced sampling method. 49 employees from service industry were studied during two periods of time (morning shift vs. late shift) across a 24-hour ambulatory monitoring. The results of multilevel-analysis showed that PA underlies a circadian rhythm as postulated. A significant difference between morning shift and late shift in NA was assigned, thus NA does not appear to be influenced by circadian rhythms. External influence in the form of work characteristics (workload, social support) was found for NA but not for PA.