This paper presents the results of an empirical case study of the characteristics of citations received by 10 open accessible non-peer reviewed working papers published by a prestigious multidisciplinary, but basically social science research institute, compared to 10 printed peer reviewed journal articles published in the same year (2004) by the same institute and predominantly by the same authors. The study analyzes the total amount of citations and citation impact observed in Web of Science (WoS) and Google Scholar (GS) received during the five-year period 2004-09 (February) by the two publication types, the citation distributions over the individual sample publications and observed years as well as over external, institutional and personal self-citations. The institute concerned is the Danish Institute for International Studies (DIIS), Copenhagen. The results demonstrate that the open access working papers publicly accessible through the DIIS e-archive became far less cited than the corresponding sample of DIIS journal articles published in printed form. However, highly cited working papers have higher impact than the average of the lower half of cited articles. Citation time series show identical distinct patterns for the articles in WoS and GS and working papers in GS, more than doubling the amount of citations received through the latter source.