This study investigates the acquisition of the unaccusative-unergative distinction in L2Japanese by English learners. The aim is to establish whether learners of Japanese are sensitive tothe lexical-semantic characteristics of verbs in similar ways as learners of Romance languages whowere found to follow the Split Intransitivity Hierarchy (Sorace, 1993a, 1995a). Two groups oflearners participated in the study, one consisting of learners who had not had any previousexposure to Japanese outside the classroom, and the other consisting of learners at the end of a9-month period of continuous stay in Japan. A control group of native Japanese speakers alsotook part in the experiment. Subjects were tested on their knowledge of the different behavior ofunaccusative and unergative verbs with respect to quantifier floating (Miyagawa, 1989); thenative group was also tested on Case drop (Kageyama, 1993). The results show that both thenative and the nonnative speakers are conditioned by the Split Intransitivity Hierarchy in theirjudgments on unergative verbs; however, their judgments on unaccusative verbs do not patternaccording to the predictions. It is argued that this difference stems from the ambiguity of theJapanese input on unaccusative verbs, which are characterized by syntactic optionality.