Carnitine is highly concentrated in the epididymis and spermatozoa, where it may serve as an intramitochondrial vehicle for the acyl group, which in the form of acyl CoA acts as a substrate for the oxidation process producing energy for sperm respiration and motility. To date, studies in rodents and humans suggest that sperm count, motility, and maturation are related to epididymal free carnitine concentrations. Moreover, supplementation with carnitine improves sperm quality and/or quantity in testes of mice exposed to physical insults, such as heat and X-irradiation, and in men with idiopathic oligoasthenospermia. These benefits may be due to increased mitochondrial fatty acid oxidation resulting in improvement in motility of epididymal sperm. The antiapoptotic effect(s) of carnitine in the testes may also contribute, but this remains speculative and requires further investigation. Research to uncover the many characteristics and mechanisms of action of carnitine in somatic and germ cells may provide insights into the pathophysiology of germ cell apoptosis, the prevention of germ cell death, and possibly specific therapy of some forms of infertility. Further well-controlled, carefully designed, larger-scale studies are necessary and desirable before widespread clinical use as an infertility therapy can be contemplated.