Although there is good evidence for implicit learning of associations between forms, little work has investigated implicit learning of form-meaning connections, and the findings are somewhat contradictory. Two experiments were carried out using a novel reaction time methodology to investigate implicit learning of grammatical form-meaning connections. Participants learned four novel articles but were not told about a critical semantic factor that determines agreement with the accompanying noun. Their task was to indicate as quickly as possible which of two pictures was being referred to by an article-noun combination. The measure of learning was whether response times would slow down when the agreement rule was violated (i.e., when the wrong article was used for the picture being referred to). Experiment 1 revealed such an effect when articles correlated with noun animacy, even for participants with no reported awareness of this regularity. In Experiment 2 no such effect was obtained when the regularity concerned the relative size of two objects. It is concluded that grammatical form-meaning connections may be learned implicitly, but learning is constrained by the nature of the meaning involved. It is argued that concepts are differentially available to implicit language learning processes.