We describe here a new approach for multilabel immunoassays. The starting point of this approach is a new nonradioisotopic immunoassay (carbonyl metallo immunoassay) based on the use of metal carbonyl complexes as tracers and Fourier transform infrared (FT-ir) spectroscopy as the detection method. We show here that the judicious choice of the organometallic tracers associated with multicomponent analysis of FT-ir spectroscopic data provides the simultaneous rapid and reliable quantitation of pmol of the organometallic tracers. The feasibility of this approach is demonstrated in the case of the two major antiepileptic drugs phenobarbital and carbamazepine.