Chronic and acute effects of L-carnitine have been recorded in a group of elite athletes by a prospective double blind placebo controlled trial. Forty top athletes (20 boys, kayak-canoë, 10 weightlifters and 10 girls, rowers) received orall 3 g L-carnitine daily for 3 weeks while 38 top athletes (20 kayak-canoë, 8 weightlifters and 10 rowers) received the same medicine as placebo. Significant changes were registered in the treated group concerning FFA and triglycerides, strength index, VO2max., urinary mucoproteins and in the control group concerning Ld (distal latency). All athletes were under medical supervision and had a controlled training program and food. The effects of a single oral dose (4 g L-carnitine were recorded in a group of 18 top weightlifters under basal conditions and 90' after L-carnitine ingestion. Significant changes in the treated group were registered for the FFA, triglycerides, urinary mucoproteins and distal latency of the right and left median nerve. Based on these data the authors recommend this aminoacid both for chronic and acute effects as a physiological mean for the biological preparation of elite athletes during hard training and competitions.