Most speakers of Irish English use a dental stop for words containing <th>, a sound that is generally pronounced as [θ] and [ð], in other varieties of English (Wells 1982; Ó hÚrdail 1997). Alveolar stops [t,d] and dental stops [
] are articulatorily and acoustically similar, and thus it is unusual for a language to use them contrastively (e.g. Ladefoged 2001). Despite this, Irish English contrasts them and speakers of this dialect have no trouble distinguishing them. This raises the question as to whether speakers of a dialect which does not use this contrast can distinguish them. To investigate this, speakers of Irish English and American English participated in an identification task involving words produced by an Irish English speaker. American English speakers had a high accuracy but did significantly worse than Irish English speakers, and both groups did significantly worse when the contrast was in final position than when it was in initial position. A small-scale production experiment examined words with this contrast and the vowel /a/, with the finding that for speakers of both dialects, the vowel is longer in words ending in <th> than <t>. The findings are discussed in the context of linguistic experience, and the effect of surrounding consonants on vowel duration.