Japan's contribution to nuclear medical research.

We investigated the degree of Japan's contribution to the nuclear medical research in the last decade. Articles published in 1991-2000 in highly reputed nuclear medical journals were accessed through the MEDLINE database. The number of articles having affiliation with a Japanese institution was counted along with publication year. In addition, shares of top-ranking countries were determined along with their trends over time. Of the total number of articles (7,788), Japan's share of articles in selected nuclear medical journals was 11.4% (889 articles) and ranked 2nd in the world after the USA (2,645 articles). The recent increase in the share was statistically significant for Japan (p = 0.02, test for trend). Japan's share in nuclear medical research output is much higher than that in other biomedical fields.