Twenty murine hybridomas were established producing monoclonal antibodies against TSH.Their immunoglobulin subclasses were IgG or IgM. The titers of T₇₄A₁₀ and T₇₁B₁₁ were 1:50 000～1:150 000 and affinity constants were 7. 15 ×10⁹L/mol and 8.75 ×10⁹L/mol respectively. The cross reactivity with HCG,FSH and LH were less than 1.1×10^-6%,0.01% and 0.016% respectively. TSH IRMA was established using T₇₁B₁₁ and T₇₄A₁₀ as tracers or solid phases.