Listening to language during the first year of life has a dramatic effect on infants’ perception of speech. With increasing exposure to a particular language, infants begin to ignore phonetic variations that are irrelevant in their native language. To examine these effects, 72 American and Japanese infants were tested at two ages, 6–8 months and 10–12 months, with synthetic versions of the American English /r/ and /l/ consonants. The /r–l/ contrast is not phonemic in Japanese. In both countries, the same experimenters, technique (head‐turn conditioning), and stimuli were used. The results revealed two significant effects. The first shows the impact of language experience on speech perception. At 6–8 months of age, American and Japanese infants did not differ. Both groups performed significantly above chance (American M=63.7%; Japanese M=64.7%). By 10–12 months of age, American infants demonstrated significant improvement relative to performance at 6–8 months (M=73.8%), while Japanese infants declined (M=59.9%). Second, performance varied significantly as a function of the direction of stimulus change (/l/ to /r/ easier than the reverse), regardless of age or language experience. Discussion will focus on separating effects attributable to linguistic and psychoacoustic factors. [Work supported by NIH.]