The syntax of referential null subjects in Brazilian Portuguese (BP) is the topic of much recent work (Kato & Negrão 2000; Ferreira 2000, 2004; Martins & Nunes 2005, 2010; Modesto 2000; Rodrigues 2002, 2004). In light of the Interface Hypothesis (Tsimpli, Sorace 2006), uninterpretable features such as purely syntactical elements should not undergo attrition. This study tests whether this theory is valid in regard to the Null Subject behavior in the production of BP speakers under influence of L2 English. In order to do so, I conducted an experiment with monolingual BP speakers and bilingual (English/BP) speakers to establish a clear-cut comparison. The experiment consisted of an elicited production task and a grammaticality judgment task. The results of the data analysis show that BP speakers under influence of L2 English do seem to indicate attrition, thus encouraging further studies questioning the Interface Hypothesis.