In many languages, tone (i.e., pitch patterns) is part of the phonological system; two words with the same sequences of segments can differ only in tone. Tone does not distinguish word meanings in English, so English-learning infants can ignore tone when learning words, but do they? We examined the encoding of tonal detail in word learning by monolingual English-learning 14- and 17-month-olds. Infants were habituated to a novel word with a Mandarin tone (/ká/) paired with a novel object. Test trials alternated between the same pairing (Same), and the same object paired with the word with a different tone (/kà/, Switch). Longer looks to the unfamiliar mapping indicate infants noticed the switch and attended to tone contrasts. Overall, neither age group discriminated the tone contrast; however, infants with larger vocabularies looked longer to the novel mapping (r=.32, p=.007), suggesting a common underlying mechanism between general word learning and tone sensitivity.