Molecular imprinting of cyclosporin A was undertaken and the resultant polymer preparation was applied to the development of a radioligand binding assay for determination of the total concentration of cyclosporin A and its metabolites. The assay method comprised extraction of haemolyzed whole blood with diisopropyl ether followed by competitive radio-‘immuno’-assay of the organic phase employing imprinted polymer particles and [3H]cyclosporin. The assay measured the parent drug and the metabolites AM1, AM9 and AM4N with equal response. Concomitant analysis of patient samples using a specific EMIT assay in parallel with this novel imprinted polymer-based assay permitted simultaneous determination of the concentration of cyclosporin A and that of its metabolites.