Fertility is dependent on a complex set of events, involving both male and female components. Normal sperm function involves many steps, including motility, capacitation, acrosome reactivity and, ultimately, fertilization of the oocyte. While male fertility is most often assessed by means of gross semen parameters, infertility may also be caused by abnormal sperm function, and only by performing specific tests of this function, may the reasons for infertility become evident. Specific tests which may be helpful include semen analysis, detailed sperm motility assessment, motility longevity, hypo-osmotic swelling test, mucus penetration assay, acrosome reactivity, antisperm antibody tests, sperm penetration assay and in vitro fertilization. Relatively well-defined syndromes of abnormal sperm function include immunologic infertility, immotile-cilia syndrome, anejaculation and nifedpine-associated infertility.