A shift from language-general to language-specific sound discrimination abilities has been largely attested in different populations of infants during the second half of the first year of life; however, data are still scarce regarding bilingual populations. Previous research with 4-, 8- and 12-month-old Catalan-Spanish bilingual infants had offered evidence of a U-shaped pattern in their ability to discriminate a language-specific vowel contrast. This research explores monolingual and bilingual 4- and 8-month-olds' capacities to discriminate two common vowel contrasts: /o-u/ and /e-u/. All groups succeeded except 8-month-old bilinguals tested on the phonetically close /o-u/ contrast. Discrimination was not facilitated when talker and token variability were reduced. A U-shaped pattern was again found when data from an additional group of 12-month-olds were included. These results confirm bilinguals' specific developmental pattern of perceptual reorganization for acoustically close vowels and challenge an interpretation merely based on a distributional account.