Described is an improved method for the measurement of TSH in blood or body liquid by immunoassays such as EIA and RIA, characterized in that TSH-P subunit specific monoclonal antibodies recognizing different epitopes are used. According to this method, TSH can easily be measured in high sensitivity with high specificity within a very short period of time without inhibition by the presence of other glycoprotein hormones such as LH, HCG and FSH. This method is useful for diagnosis of various diseases in which TSH plays a role, such as proto- phathic hypothyroidism, Basedow's disease and cretinism.