Chicken spermatozoa undergo a post-testicular maturation process similar to that reported for mammals. Association of secreted epididymal proteins and glycoproteins with the sperm surface appears to be complete at the anterior ductus deferens. However, antigenic change to, and glycosylation and deglycosylation of seminal plasma and sperm surface-associated proteins, selective loss of proteins from the sperm surface, as well as secretion of some seminal plasma proteins and selective absorption of others by epithelial cells lining the excurrent ducts, continues in the ductus deferens and ampulla. Hypertonic treatment or neuraminidase treatment of spermatozoa without apparent loss of sperm integrity in-vitro, reduced the ability of spermatozoa to gain access to the uterovaginal insemination. This indicates a clear role for sperm surface-associated proteains and sperm surfarce sialic acid in vaginal sperm transport. Sperm surface-associated proteins were also extracted by glycerol in a temperature-dependent and concentration-dependent manner. This was accompanied at room temperature by a glycerol concentration-dependent reduction in sperm motility. These effects may be implicated in the contraceptive action of glycerol in the chicken vagina. Spermatozoa from several avian and mammalian species entered quail uterovaginal junction SSTs in-vitro, and turkey spermatozoa were found in chicken uterovaginal junction SSTs following uterovaginal junction but not intravaginal insemination, thus showing that the SSTs are not selective, and identifying the vagina as a major site of oviducal sperm selection. Spermatozoa washed from the vagina following intravaginal insemination had immunoglobulin bound to their surface, which was shown to be associated with cell death. Spermatozoa recovered from the anterior oviduct however, were generally devoid of bound immunoglobulin. Furthermore, sperm access to the newly ovulated egg in-vivo following incubation with vaginal mucosa in-vitro did not differ significantly from that of control spermatozoa despite fewer viable spermatozoa inseminated, suggesting a true 'selection' of spermatozoa in the vagina. Ovarian pocket fluid, postulated to be the milieu in which fertilisation takes place in-vivo, altered sperm surface antigenicity and reduced sperm motility in-vitro, suggesting that spermatozoa may naturally undergo oviduct-induced changes prior to fertilisation. Sperm-egg interaction appears specific and receptor-mediated, as in mammals. Spermatozoa showed no preference for the animal pole of the egg, and heterologous gamete combinations indicated limited, order-dependent rather than species-dependent specificity. Presenting carbohydrate residues on the sperm surface and sperm surface antigenicity showed a lack of change proportional to species divergence, although the vagina clearly presents the main barrier to interspecies fertilisation within the order Galliformes.