The emission and reflection spectra of ZnO have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Free-exciton emission is observed for the first time. Both the ${\ensuremath{\Gamma}}_{5}$ and ${\ensuremath{\Gamma}}_{6}$ state excitons associated with top valence band have been identified. This identification has established the valence-band symmetry ordering in ZnO.