For the development of multilayer fluorescent immunoassays to determine directly a variety of therapeutic drugs high specific monoclonal antibodies against the anticonvulsants carbamazepine, phenobarbital, phenytoin and valproic acid have been prepared. For each antibody a standard curve could be established showing good linearity and a suitable sensitivity scope. To validate the eligibility of the desired antibodies a variety of drugs and metabolites sharing structural similarities to the individual drugs were tested for their cross-reactivity. It could be shown that only a few very closely related compounds exhibited substantial cross-reactivity. These monoclonal antibodies are therefore assumed to be suitable for a TDM-assay development.