SummaryThe work described is concerned with the study of vocal fold vibration before, during and after treatment in twenty patients suffering from a variety of medically diagnosed disorders. Voice quality was assessed with the help of both standard qualitative laryngologists' and speech therapists' judgements and patients' opinions, and of the output waveform of the laryngograph.Previous work (Abberton and Fourcin, 1972;Fourcin and Abberton, 1971;Fourcin, 1974) suggested that these waveforms (Lx) might show characteristic features of certain vocal fold disorders. The present study is an attempt at providing further information in this direction.