Radioimmunoassay of thyrotropin (TSH) is well-established, and highly sensitive radioimmunometric assay is often used clinically (1). Some recent results indicate that TSH immunoreactivity and bioactivity are not always synonymous (2). The detection limit of present bioassays for bovine TSH is about 0.5-1 milli-int. unit/L (3-6). More-sensitive bioassay is necessary for evaluating human TSH. Th...
