This experimental study investigates the differential effects of three conditions (nonnegotiatedpremodified input, negotiation without “pushed output” [Swain, 1985],and negotiation plus pushed output) on L2 learners' vocabulary comprehension andacquisition (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) onlynegotiated interaction that incorporated pushed output appeared to have promoted both receptiveand 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 negotiationwithout output, but it was more effective in promoting productive acquisition. The findings of thisstudy provide empirical evidence for the important role of negotiation in facilitating thecomprehension and acquisition of L2 vocabulary, which suggests that output plays a key rolewithin the negotiation process for productive lexical acquisition.