The permanent poling effects of L-alanine substitution on the pyroelectric properties of T. G. S. are summarized. The observations are explained in terms of a structural model in which ferroelectric switching is impeded by the lack of the required prototypic symmetry in the substituent molecule. Other active and passive additives may be proposed from the model. Much of the recent interest in T. G. S. is related to use in radiation detectors using the pyroelectric effect. The combination of moderately high pyroelectric coefficient and low dielectric constant at room temperature, together with the ease with which large optical quality single crystals can be grown from solution, are some of the properties that make T. G. S. superior to other materials for many detector applications. The effective pyroelectric output of any ferroelectric crystal depends on its degree of poling. The major disadvantage of using ferroelectric crystals as pyroelect~ics is the possibility of a single domain crystal becoming rnultidomain or depoling in use. However, it was found recently by Lock [I] that T. G. S. crystals grown from a solution containing between 2 and 35 % alanine (a) show a permanent self bias. Dielectric hysteresis loops of such crystals are distinctive in that they are partially or completely displaced along the field axis (see Fig. la). It was found that the crystals containing alanine retained their self bias even after prolonged heating above the Curie