Maternal responsiveness has been positively related with a range of socioemotional and cognitive outcomes including language. A substantial body of research has explored different aspects of verbal responsiveness. However, perhaps because of the many ways in which it can be operationalized, there is currently a lack of consensus around what type of responsiveness is most helpful for later language development. The present study sought to address this problem by considering both the semantic and temporal dimensions of responsiveness on a single cohort while controlling for level of parental education and the overall amount of communication on the part of both the caregiver and the infant. We found that only utterances that were both semantically appropriate and temporally linked to an infant vocalization were related to infant expressive vocabulary at 18 mo.