This article addresses the role of previously acquired languages in the acquisition of a third language (L3) in two experimental studies on object expression in Brazilian Portuguese (BP). Participants were English-speaking learners of BP as L3 with knowledge of Spanish as a second language (L2) and Spanish-speaking learners of BP with knowledge of English as L2. Like Spanish, BP has object clitic pronouns, but there are important differences between the two languages with respect to the rates of clitics used in spoken and written registers, null objects and the position of clitics with respect to the verb. English, by contrast, lacks object clitics. Study 1 tested use of clitics and other objects in an oral production task. Study 2 tested knowledge of clitic placement in a written acceptability judgment task. The general results of the two studies show that acquisition of Brazilian Portuguese object expression is not very problematic but there are transfer effects from Spanish (as L1 and L2) in the two experimental groups. This result suggests that structural similarity or cross-linguistic correspondences matter in L3 acquisition. (Contains 12 tables, 7 figures and 27 notes.)