Purpose – The purpose of this study is to identify and examine the factors that affected the scale of ILL photocopy requests between Japanese university libraries from 1994 to 2008. Design/methodology/approach – Based on the newly developed conceptual framework to interpret the rise and fall in ILL, more than 10 million requests, sent through a nation-wide system called NACSIS-ILL from 1994 to 2008 were quantitatively analyzed. Findings – The number of photocopy requests for articles in foreign journals started to decrease in 2000, due to the dramatic increase of e-journal titles made accessible through “Big Deal” contracts that came into effect in 2002 as well as other similar trials prior to it. On the other hand, requests for articles in domestic journals, mostly written in Japanese, continued to increase until 2006. The main factor for this increase was the expansion of journal title coverage in bibliographic databases, which enabled users to retrieve more references. However, requests decreased in 2007, because of advances in digitization in the Japanese academic environment. Research limitations/implications – This research proposes a conceptual model to understand document demand and service patterns observed in nation-wide ILL services. It also successfully draws a comprehensive picture of ILL in Japanese higher education institutions, based on more than 10 million request records over 15 years, and it shows how the number of ILL requests correlates with the availability of requested journals in electronic form. Originality/value – This research proposes a conceptual model to understand document demand and service patterns observed in nation-wide ILL services. It also successfully draws a comprehensive picture of ILL in Japanese higher education institutions, based on more than 10 million request records over 15 years, and it shows how the number of ILL requests correlates with the availability of requested journals in electronic form.