The importance of perceptual phenomena in nasal vowel development is well known, but only recently has attention turned to suprasegmental phenomena known to condition this development. Perceptual explanations have already been given for the conditioning effect of vowel length, and, more tentatively, stress. In this study, we provide data from perceptual experiments in which nasality judgements were obtained from English speakers to examine the conditioning effects of three suprasegmental phenomena, all related to stress. The perceptual basis of the stress parameter is confirmed, however, no evidence is found of a similar effect underlying observed differences in nasalisation between pre and post-tonic vowels. Most importantly, foot structure is shown to condition nasality judgements such that vowels in single syllable feet (oxytones) are judged as more nasal than those in trochaic (paroxytonic) feet. Both the stress and the foot structure effects are shown to be independent of the vowel-length.