Experimental and clinical data reported in the literature emphasize the important role that immune factors may play in the genesis of male infertility even if many problems still remain to be solved. Auto or homo-sensitization in animals (and in male volunteers) can be obtained with testicular homogenate or epididymal spermatozoa and complete Freund's adjuvant. Immune orchitis in spontaneous human pathology has also been reported. Vasectomy for the voluntary control of male fertility may be considered a particular form of experimental autoimmunization; and many vasectomized individuals develop antisperm antibodies in blood serum and/or in seminal plasma. In spontaneous male infertility antisperm antibodies can: (i) be a mere epiphenomenon; (ii) be a factor aggravating a pathologic situation already able to cause infertility; (iii) play a pathogenetic role in some forms of so-called idiopathic infertility and so could be defined as infertility due to antisperm antibodies. If the antisperm autoimmune reaction represents the casual factor of infertility, corticosteroid therapy seems to give the most satisfactory results, administered either in high doses for a very short time period or in low doses over a prolonged period, or even after transient pharmacologically induced azoospermia.