Current status of reproductive function in Japanese fertile men: international collaborative project on a study of partners of pregnant women.

The data on reproductive function in 255 Japanese fertile men resident in the Kawasaki/Yokohama area in Japan were described. The sperm concentration was 107.9 +/- 97.4 x 106/mL. The semen volume was 3.2 +/- 1.5 mL and percentage motile spermatozoa (grade A + B in WHO criteria) was 56.8% +/- 14.7%. The evidence for secular changes in semen quality and other changes in male reproductive health is inconclusive, although regional differences would appear to be stronger. The present study is the first large-scaled prospective survey on the reproductive function of Japanese normal men proven fertility, which was planned as an international comparative study.