To check whether the recently proposed SRBRF model also adequately describes the relaxor to ferroelectric transition the temperature dependence of the static dielectric constant of PMN has been fitted to the SRBRF model. The results show that in contrast to dipolar glasses the mean coupling constantJ0is here indeed close to the root mean square varianceJ. ForE⩾EC J0can therefore become bigger thanJresulting in a transition from a relaxor to a ferroelectric state. The relaxor to ferroelectric cross-over in the non-linear dielectric responsea3=&khgr;3/&khgr;l4in the form predicted by the SRBRF model forE⩾EChas been observed in PLZT ceramics. The temperature dependence of the Edward-Anderson order parameterqhas been determined via NMR in PSN in the region of the ferroelectric transition and as well shows theT-dependence predicted forJ0>J.The relaxor to ferroelectric transition can be thus well described by the SRBRF model. ©2000 American Institute of Physics.