L-carnitine is concentrated in the epididymis, where sperm mature and acquire their motility (86). Two uncontrolled trials of L-carnitine supplementation in more than 100 men diagnosed with decreased sperm motility found that oral L-carnitine supplementation (3 grams/day) for three to four months significantly improved sperm motility (87, 88). However, no information on subsequent fertility was reported. A cross-sectional study of 101 fertile and infertile men found that L-carnitine concentrations in semen were positively correlated with the number of sperm, the percentage of motile sperm, and the percentage of normal appearing sperm in the sample (89), suggesting that L-carnitine levels in semen may be useful in evaluating male infertility. More recently, a placebo-controlled,double-blind, cross-over trial in 86 patients with male infertility found that L-carnitine (2 grams/day) supplementation for two months led to significantly improvements in sperm quality, evidenced by increases in sperm concentration and motility (90). Similar improvements in sperm motility were observed in a subsequent placebo-controlled, double-blind, randomized study conducted by the same group, but the patients received combination therapy consisting of L-carnitine (2 grams/day) and acetyl-L-carnitine (1 gram/day) for six months (91). Interestingly, in both studies, the most dramatic carnitine-induced improvements were noted in patients with the lowest baseline sperm motility measures (i.e., most severe cases) (90, 91). Another group of researchers also reported improved sperm motility following combined carnitine therapy. In this placebo-controlled, double-blind, randomized study, 44 patients with idiopathic asthenozoospermia (reduced sperm motility) received placebo, L-carnitine (3 grams/day), acetyl-L-carnitine (3 grams/day), or a combination of L-carnitine (2 grams/day) and acetyl-L-carnitine (1 gram/day). The combination therapy as well as acetyl-L-carnitine, alone, resulted in significant increases in sperm motility (92). Together, these data suggest that carnitine therapy may be useful in disorders of sperm motility and male infertility; however, large-scale clinical trials are undoubtedly necessary.