In addition to in-vivo methods, numerous in-vitro methods have caught on for the analysis of signaling pathways in recent years. One of the methods which is becoming increasingly common is reverse-phase microarrays, which involves taking the extract from cells, e.g. from a biopsy or cells with and without stimuli, and spotting them on slides in a concentration series and incubating with specific antibodies (e.g. phospho-specific antibodies). The signal intensity makes it possible to draw conclusions about protein changes, such as the abundance of proteins or post-translational modifications. The advantages of microarrays are the small sample volume, the high number of technical replicates and the ability to test a great many samples under identical conditions. This makes it possible to investigate time progressions and analyze the signaling pathways or the »reaction« of cells (tissue) to external stimuli, in order to then draw conclusions about the mechanism of action.