A study of thyroid stimulating activity in human serum with the highly sensitive cytochemical bioassay.

The cytochemical bioassay is able to detect minute amounts of thyroteopin and thyroid stimulating immunoglobulins. Estimations of serum TSH by the cytochemical bioassay are in good agreement with values obtain by radioimmunoassay. In untreated hyperthyroid patients with Graves' disease the TSH levels are significantly lower than in control subjects. Thyroid stimulating immunoglobulins showed a delayed time corse of action in the bioassy and this provided a voncenient method of distinguishing between the two thyroid stimulators.