John Aitken's research has elucidated fundamental cellular and molecular mechanisms regulating mammalian sperm function, fertilisation and early embryonic development. Demonstrating that oxidative stress, due to electron leakage, plays a major role in defective sperm function, his work linked this pathway to DNA damage and provided the basis for anti-oxidant therapy. Using proteomic approaches, he has identified a number of novel mediators of sperm-egg interactions. These studies unravelled new mechanisms which prevent sperm degeneration by blocking apoptotic pathways. Based on this information, his work provides opportunities to improve fertility and also pathways for new contraceptive development.