It is well known that vowel duration may differ across languages. In foreign language learning these differences may lead to incorrectly produced durations in the target language, since the speaker will be inhibited by his mother tongue. In this paper two experiments are reported. The first describes a production test, aimed at obtaining a systematic description of durations of comparable vowels in RP British English and Dutch, as well as English spoken by Dutch foreign learners. The data show considerable differences in vowel duration between native English, foreign English, and native Dutch. The differences found between native and foreign English were used in a second perception experiment to investigate the relevance of incorrectly produced vowel durations to the perception of a foreign accent. Results show that native listeners are more sensitive to changes in the spectral composition of the speech signal than to changes in vowel duration.