Abstract: The present invention relates to new cytochemical and histochemical detection methods based on the enzymatic activity of poly-ADP-ribose-polymerases (PARP). In particular, the present invention provides methods and systems for cytochemical or histochemical detection of a molecule of interest based on detecting poly-ADP-ribose (PAR). Further, the present invention provides methods for screening for compounds altering the amount of NAD or analogs thereof in subcellular compartments based on detecting the amount of PAR formed in said subcellular compartment as well as methods for determining the spatial distribution of a molecule of interest. In a further aspect, the present invention provides systems and kits for conducting said methods as well as a new expression vectors suitable for said systems.