Abstract: The fifth edition of the World Health Organization （WHO）manual for semen analysis includes for the first time reference values for human semen characteristics. This paper considers whether such values will help to resolve the intensely debated data indicating temporal and geographical shifts in sperm counts and hypotheses that anthropogenic activities that result in the release of chemicals into the environment are detrimental to male reproductive health. The reasons that these reference values will not fulfil these purposes are also explained. Although established reference values for semen characteristics are of limited value in analytical epidemiologic research，the WHO guidelines are of utmost importance for supporting the development of appropriate research protocols. Moreover，in spite of its limitations，semen analysis is still a useful research tool in epidemiological research，and no superior alternatives are on the horizon.

Key words: Decline, Epidemiology, Reference values, Research, Semen analysis, Sperm counts