Second-harmonic light generation and birefringence data are reported for KTaO3:Na. They are evaluated in terms of an inhomogeneous lattice polarization. The correlation of polar orientation is shown to extend to hundreds of Å in the paraelectric phase of KTaO3:Na. A sharp increase of the correlation length for 15% Na doping to 1500 Å is associated to the polar transition at 12 K. From the low-temperature value of the correlation length, conclusions are drawn about the nature of the polar phase. © 1989, IOP Publishing Ltd.