Carnitine is present in very high concentrations in the epididymides, which is used to store and transport sperm. Carnitine could protect spermatozoa from oxidative damage and thus improve sperm quality. The results of a study including 52 men with idiopathic infertility confirm this hypothesis: the subjects were divided into two groups and received either clomiphene (an anti-estrogenic drug) or 2 g of L-carnitine per day for three months. Both substances increased the number and mobility of spermatozoa.
Moradi M. Safety and efficacy of clomiphene citrate and L-carnitine in idiopathic male infertility. Urol J 2010; 7(3):188-93.