The pressure dependence of the elastic constants C-ij of GaP have been meas
ured up to 15 GPa in a diamond anvil cell. Brillouin backscattering experim
ents along the principal crystallographic directions yielded four combinati
ons of elastic constants from which the three independent C-ij were extract
ed. Above 15 GPa the closure of the energy band gap prevents the detection
of the signal. [S0163-1829(99)04827-4].