The development of individual, highly sensitive assays allows quantitative drug and metabolite analyses for numerous applications ranging from cell systems (intra- and extracellular)and small animal models (pharmacokinetic determinations in serum/plasma/blood as well as distribution in tissues) to brain tissues from small animal studies that determine the blood/brain barrier permeability. Our assays, especially the developments for new drug candidates, allow the establishment of pharmacokinetic data (AUC, Cmax, Tmax, T1/2, VD, Cl) from animal studies, which are essential for assessment of pharmacological properties.