This research studies the use of metadiscourse in research articles in different cultures, disciplinary areas and article sections, aiming at investigating how this rhetorical device varies in different linguistic and socio- cultural contexts, contributes to the construction of meaning in written texts and reflects the construction of knowledge in different disciplinary areas. This work adopts as theoretical basis a sociointeractional approach to language, the theory of social construction of knowledge and principles of contrastive rhetoric. The research corpus is composed of 24 scientific articles, divided into two languages (Portuguese and English), two disciplinary areas (Biomedical Sciences and Linguistics, Letters and Arts), and four sections (Introduction, Methodology, Results and Discussion). The study of variation between texts written in English and Portuguese shows that there are differences in the use of metadiscourse items which can focus on micro or macroorganization of the scientific article. Interdisciplinary variation shows that scientific texts can be written either in a subjective or objective manner, and that knowledge construction in different disciplinary communities can be based either on ideas or facts. As to research article sections, this study shows that the use of metadiscourse varies according to writers´ intention to reach rhetorical objectives in each section. This research study reinforces both the possibility and necessity to focus on metadiscourse and language under a sociointeractional perspective, confirming that academic writing is interactive, and showing that the construction of meaning in texts and the construction of knowledge vary in different cultures and disciplinary communities.