In research on Spanish subject pronoun expression, Spanish-English bilinguals have been shown to present higher rates of expressed subjects in code-switching than in monolingual Spanish mode, an outcome attributed to perseveration from English or to convergence with English. In this study we seek to arbitrate between these competing accounts. For that purpose, productions were elicited from bilinguals in an oral elicitation task, manipulating perseveration source and target structures in three modes: monolingual Spanish, language switching, and code-switching. Participants demonstrated the anticipated sensitivity to perseveration across conditions and effects of bilingual mode in the code-switching condition, with greater expressed pronoun use with omitted subject primes. These results allow us to isolate structural perseveration from bilingual effects and to ascribe the source of increased use of expressed pronominal subjects in bilingual Spanish to dual language activation or convergence.