We present resonant femtosecond pump-probe reflectance measurements of exci
tons in high quality wurtzite GaN epilayers for a range of lattice temperat
ures and various pump intensities. From the density dependence of the excit
onic bleaching we find that the Mott density is n(Mott) less than or equal
to 2.2 x 10(19) cm(-3). At 4 K we find that the exciton dynamics is dominat
ed by trapping at defects via acoustic phonon emission on a timescale of si
milar to 16 ps. At temperatures above 60 K we observe a much longer relaxat
ion component of similar to 350 to 400 ps, which we ascribe to the radiativ
e recombination of free excitons.