The annoyance-reaction is one of the central variables in noise research. After an introduction to different concepts and definitions of noise annoyance different scales of how noise annoyance can be measured are shown. The question is discussed whether disturbance effects of noise at different times of day are given. To clarify this problem, the results of a series of actual German noise studies are reported. In these studies differences between day- and night-time annoyance are found depending on the sound sources. For the case of road traffic noise no differences between day and night-time annoyance were found. In contrast, annoyance reactions are related to the time of day for railway and air traffic noise ...