Adult second-language (L2) learning is often claimed to be slow and laborious compared to native language (L1) acquisition, but little is known about the rate of L2 word learning. Here we report that adult second-language learners' brain activity, as measured by event-related potentials (ERPs), discriminated between L2 words and L2 'pseudowords' (word-like letter strings) after just 14 h of classroom instruction. This occurred even while the learners performed at chance levels when making overt L2 word-nonword judgments, indicating that the early acquisition of some aspects of a new language may be overlooked by current behavioral assessments.