This study examines whether aural processing of input in a situation of implicit instruction can build a knowledge base that is available for both comprehension and production tasks. Fifty-five Dutch students learned a miniature linguistic system based on Spanish. Three training conditions were compared in which noun-adjective gender agreement was the learning target. The first group of participants received receptive training, the second group received receptive and productive training, and a third group served as a control. The control group received no training of the target structure and only read an explanation of the target structure rule. Receptive knowledge was assessed with a self-paced listening test, a match-mismatch test, and a grammaticality judgment task. Productive knowledge was tested with a picture description task in single- and dual-task conditions. A postexperimental questionnaire tested whether any explicit knowledge had been induced. Results suggest that the receptive and receptive + productive training programs succeeded in building a knowledge base that was used in comprehension but much less so in production. These results will be interpreted in light of processing and the distinction between implicit and explicit knowledge. (Contains 1 footnote.)