Pb(Sc1/2Ta1/2)O-3 ceramics have been characterized by dielectric measurements in a wide range of frequencies (10(2)-10(9) Hz). A strong dispersion occurs with two low and high frequency contributions below the transition temperature. Only high frequency relaxation is still observed at high temperature. A microscopic model of correlated chains was used in order to explain the latter relaxation. Dipole correlations at low temperature are responsible for the low frequency dispersion. A minimum in the high frequency relaxation appears at the transition temperature. Identical results have been observed for a Pb(Sc1/2Nb1/2)O-3 ceramic.