On the basis of reported experimental and clinical studies we investigated the effectiveness of L-carnitine administration in a group of patients with idiopathic asthenospermia. A favourable effect of the compound on sperm motility and rapid linear progression has been shown in 37 out of 47 patients treated. In addition, the total number of sperms increased. L-carnitine was supplemented orally by a daily dosage of 3 g for three months.