Cyclosporin C-hemisuccinate was coupled to thyroglobulin by the mixed anhydride method. Cyclosporin C was used instead of cyclosporin A (CsA) because of lack of functional groups of CsA. The resulting protein-cyclosporin C conjugate allowed us to induce high antibody titers also against cyclosporin A in rabbit and mice. Polyclonal and monoclonal antibodies were prepared following standard procedure. Since no standard methods for screening and quantification of anti-CsA-antibodies were available, two methods were adapted: (a) liquid phase radio assay (RA) and (b) solid phase enzyme-linked immunoassay (ELI-SA). For the former procedure inactivated charcoal was applied to separate the antibody-bound and the unbound CsA. CsA-coated PVC microtiter plates were used for the latter.