The peripheral auditory system acts as an array of bandpass filters. Temporal information at the output of each filter can be classified as temporal fine structure (TFS), the rapid oscillations close to the filter centre frequency, and temporal envelope, modulations in amplitude superimposed on this TFS. The roles of TFS in the perception of complex tones and speech were investigated for normal-hearing (NH) and hearing-impaired (HI) subjects. The discrimination of harmonic and frequency-shifted bandpass-filtered complexes was used as a measure of TFS sensitivity. HI subjects were much less sensitive to TFS in complex tones than NH subjects, with many HI subjects scoring no better than chance when only TFS cues were available for discrimination. The use of TFS information in speech was assessed using a speech signal that was split into a large number of frequency bands, which were either vocoded, to contain only temporal envelope information, or unprocessed, and so contained both envelope and TFS information. The importance of TFS at different spectral regions in speech was investigated. NH subjects benefited similarly from TFS added to each of the spectral regions tested (spanning 100-8000 Hz). HI subjects showed no significant benefit when TFS was added to the whole spectrum. Finally, a processing scheme that removed temporal envelope cues, leaving TFS cues relatively intact, was assessed. Together, these experiments suggest that TFS information is important for speech perception when listening in fluctuating background noise. The relative insensitivity of HI subjects to TFS may partly account for their particular difficulties listening to speech in such environments.