In the last few years, the application of chromatographic and other modern techniques to the problem of isolating TSH has led to further purification (Bates and Condliffe, 1960; Pierce, Carsten and Wynston, 1960). The most active preparations obtained by these two groups of investigators appear to be similar in potency, composition and physical properties.

Two problems present themselves in considering any hormone in blood. First, is the circulating form of the hormone the same as that found in the gland where it is synthesised and stored? Second, what is its concentration in normal circumstances and in what circumstances will this concentration depart from the normal level and in which direction? It is therefore necessary to consider the properties of pituitary TSH if the fragmentary chemical information about blood TSH is to be discussed rationally. The importance of knowing in what chemical forms the hormone may exist is accentuated by the recent observation that there exists an abnormally long-acting TSH in blood drawn from many thyrotoxic patients (Adams, 1958). Whether this abnormal TSH differs chemically from pituitary TSH, or is, alternatively, normal TSH with its period of effectiveness modified by some other blood constituent, cannot be decided without chemical study of the activity in the blood of these patients and a comparison of the substance responsible for the blood activity with pituitary TSH.