The interband optical transitions in single-crystal GaN films grown by metal organic chemical vapor deposition have been studied at 10 K and room temperature using nondegenerate nanosecond optical pump-probe techniques. At low temperatures, strong, well-resolved features are seen in the absorption and reflection spectra corresponding to the1sA and B exciton transitions. These features broaden and decrease in intensity due to the presence of a high density of photoexcited free carriers and are completely absent in the absorption and reflection spectra as the excitation density,Iexc,approaches3 MW/cm2,resulting in induced transparency in transmission measurements. The absorption spectra also show induced absorption below the band gap asIexcis increased. Both the observed induced transparency and induced absorption were found to be extremely large, exceeding4×104 cm−1as the pump density approaches3 MW/cm2at 10 K. ©1998 American Institute of Physics.