Room-temperature photoreflectance spectroscopy is performed on a series of GaN-AlGaN quantum wells grown by molecular beam epitaxy. We show that the potentialities of this powerful investigation method previously demonstrated to many low-dimensional systems can be extended to nitride-based quantum wells for accurate large scale characterisation. In particular, this technique allows us to get rid of optical interferences that usually prevent the observation of free-exciton transitions below the band-gap of GaN. Such transitions occur in wide quantum wells, because of large built-in electric fields which also quench the oscillator strength of the transitions. Also, this technique allows us to magnify the features of confined excited states, which are difficult to observe by standard reflectance. (C) 1999 Elsevier Science Ltd. All rights reserved.