The availability of scientific and intellectual works freely through scientists' personal web sites, digital university archives or through the electronic print (eprint) archives of major scientific institutions has radically changed the process of scientific communication within the last decade. The “Open Access” (OA) initiative is having a tremendous impact upon the scientific communication process, which is largely based on publishing in scientific periodicals. This exploratory paper investigates the research impact of OA articles across the subject disciplines. The research impact of OA articles as measured by the number of citations varies from discipline to discipline. OA articles in Biology and Economics had the highest research impact. OA articles in hard, urban, and convergent fields such as Physics, Mathematics, and Chemical Engineering did not necessarily get cited most often.