Raman scattering by coupled LO phonon-plasmon modes in p-type GaN layers has been measured for different hole densities up to 3 x 10(18) cm(-3) Both axial and planar coupled modes were clearly observed. The breakdown of usual selection rules for the planar mode is discussed. The lineshape analysis of coupled modes was achieved in the frame of a dielectric model, using electrical data from Hall measurements; in this calculation we used the value of the Faust-Henry coefficient determined from Raman intensity measurements on the LO and TO phonons. A good fit of the experimental data is obtained and gives evidence for hole mass anisotropy. (C) 1998 Elsevier Science Ltd. All rights reserved.