Male infertility, while having a variety of causes, is generally discussed in terms of semen parameters. While the World Health Organization (WHO) have been able io set limits for semen parameters below which a male can be considered subfertile (20 million/ml; >50% motility; >50% morphologically normal forms), it is well documented that in vivo conceptions have been achieved where semen quality falls well outside these limits, and that infertile men may have normal semen parameters. Macleod and Gold in comparing 1000 fertile men and 1000 infertile men, found that significantly more infertile men had sperm densities below 20 million/ml, but also that 60% of infertile men had sperm densities of 60 million or more. Jouannet and Feneaux have shown that the conception rate in vivo only apparently falls significantly at sperm concentrations of less than five million/ml. Although the cause of subnormal semen analysis is unknown in the majority of cases, there is no reason to suppose that abnormal semen parameters on their own are the cause of infertility. Rather the problem may be caused by failure of sufficient numbers of sperm traversing the female tract and reaching the oocyte. Unfortunately, lack of defined diagnoses lead to a lack of direct treatment for subnormal semen parameters. The development of in vitro fertilization (IVF) resulted in a method that could be used to circumvent the problem since it requires relatively low numbers of sperm and these are placed in the immediate vicinity of the oocyte. It should also be pointed out that normal semen parameters do not imply fertility, since these parameters cannot directly identify dysfunction. IVF offers the advantage that sperm-oocyte interractions can be observed, and in cases of fertilization failure, the point at which sperm dysfunction manifests itself may potentially be identified – if not the nature of the dysfunction. Techniques have now been developed that may overcome certain types of dysfunction, using both biochemical and mechanical means.