Previous research has found that children who are acquiring argument-drop languages such as Turkish and Chinese make use of syntactic frames to extend familiar verb meanings (Göksun, Küntay & Naigles, 2008; Lee & Naigles, 2008). This article investigates whether two-year-olds learning Japanese, another argument-drop language, make use of argument number and case markings in learning novel verbs. Children watched videos of novel causative and non-causative actions via Intermodal Preferential Looking. The novel verbs were presented in transitive or intransitive frames; the NPs in the transitive frames appeared ‘bare’ or with case markers. Consistent with previous findings of Morphosyntactic Bootstrapping, children who heard the novel verbs in the transitive frame with case markers reliably assigned those verbs to the novel causative actions.