A study investigated whether second language (L2) learners' participation in negotiation with native speakers (NSs) meets their needs for data on L2 lexical and structural features. The question was addressed through an analysis of NS utterances of negotiation that were produced as 20 native speaker-non-native speaker (NS-NNS) dyads carried out four communication tasks in English. The analysis revealed that the NS utterances of negotiation offered data on L2 forms, the meanings they encoded, and some of the structural relationships into which they could enter. Negotiation thereby served the NNSs in ways that supplemented its two most widely acknowledged contributions to the L2 acquisition process, i.e., NNS comprehension of L2 input and modification of interlanguage output. However, the analysis also revealed that the NS utterances of negotiation contained few explicit cues that could help the NNSs distinguish between lexical and structural features of their interlanguage that were target-like and those that were not. Thus negotiation appeared to address NNS needs for data on features that were part of the L2, but offered no explicit information on which of their own interlanguage features did not belong to the L2. Contains 53 references. (Author/LB)