This experimental study investigates the differential effects of three conditions (nonnegotiated premodified input, negotiation without “pushed output” [Swain, 1985], and negotiation plus pushed output) on L2 learners' vocabulary comprehension and acquisition (receptive and productive). Analyses of variance performed on the data indicated that: (a) negotiated interaction had a positive effect on the comprehension of L2 words; (b) only negotiated interaction that incorporated pushed output appeared to have promoted both receptive and productive acquisition of words as well as an increase in productive word retention; and (c) negotiated interaction plus output did not promote receptive acquisition more than negotiation without output, but it was more effective in promoting productive acquisition. The findings of this study provide empirical evidence for the important role of negotiation in facilitating the comprehension and acquisition of L2 vocabulary, which suggests that output plays a key role within the negotiation process for productive lexical acquisition.