This study tests the hypothesis that function words are among the earliest word forms segmented by preverbal infants. In a visual fixation procedure, French-learning 8-month-old infants were familiarized to a function word, mes or ta. All infants were then tested with passages containing mes vs. ta. Looking times during the presentation of the two passage types were expected to differ if infants segmented the target functor. The results showed a significant interaction of passage type and sex. Although the direction of the looking preference is different for the two sexes, both groups showed a significant difference in listening times to the passage containing the target versus that containing the non-target. This suggests that both groups segmented the function words. The implications of functional elements for early lexical and syntactic acquisition are discussed.