Some immunological aspects of male infertility are discussed, including the mechanism of induction of auto-antibodies to sperm-specific antigens. Tests to determine antispermatozoal antibodies in serum are discussed. Since there is no direct relation with infertility, more attention is focused on the presence of antispermatozoal antibodies in semen. These antibodies affect male fertility by reducing the capacity of the spermatozoa to penetrate cervical mucus. This penetration inhibition is caused by autoagglutination of the spermatozoa in the ejaculate and by the shaking phenomenon. The sperm-cervical mucus contact test, based on the shaking phenomenon is described. The use of the Mixed Antiglobulin Reaction tests, to detect IgG and IgA antibodies on spermatozoa is discussed. Finally, the effect of antispermatozoal antibodies on the fertilization process is reviewed.