The novel coupling method based on the hyphenation of immunoreaction with ICP-MS was developed and applied to the determination of thyroid-stimulating hormone (TSH) in human serum. In this system, TSH was firstly captured by anti-TSH monoclonal antibodies immobilized on a solid support. Biotinylated anti-TSH monoclonal antibodies and Eu3+-labelled streptavidin were then added to form the complex, captured antibody–TSH–biotinylated anti-TSH antibody–Eu3+-labelled streptavidin. After unbound reactants were washed away, Eu3+ bound to the complex was extracted by 1% HNO3 and measured by ICP-MS. The Eu signal was directly proportional to the serum TSH concentration. The limit of detection was 0.5 mIU L−1 and the assay was linear up to 170 mIU L−1. The within-run (n = 6) and between-run (n = 6) relative standard deviations (RSD) for low, medium and high concentration standards did not exceed 10%. The TSH results obtained by this procedure correlated well with those obtained by radioimmunoassay (r2 = 0.9639).