The effects of dental appliances on speech were studied when subjects wore the appliances, both in quiet and in the presence on an intense noise. A group of 24 normal-speaking subjects read lists of syllables, words, and sentences and spoke spontaneously in each of six appliance and noise conditions. Several acoustic and perceptual measurements were made in each condition. In general, speech deteriorated when appliances were placed and when noise was presented. The type and amount of speech disruption varied as a function of speech task and aspect of speech. There was no evidence that the effects of appliances on speech differed in quiet and noise conditions. Inter-subject variability was large.