OBJECTIVE Several studies have been published in recent years which suggest that L-carnitine supplementation can influence the lipid metabolism in some species and can also affect body composition of growing animals. Only few results are available so far on the effect of L-carnitine supplementation on weight reduction and body composition of animals fed an energy-deficient diet. The aim of this study was therefore to investigate whether L-carnitine supplementation combined with an energy-deficient diet can influence weight development and body composition. METHODS An experiment was conducted with 36 rats with an initial body weight of about 460 g. One-third of the rats were killed, the remainder were divided into two groups (control group, treated group) and fed a semi synthetic diet at an energy level of about half of the rats' maintenance requirement. The basal diet was essentially carnitine-free. The diet of the treated group was supplemented with L-carnitine (5 g/kg). The feeding period extended over 23 days. Experimental parameters were weight loss, composition of carcass and weights of the fat pads surrounding the kidneys, intestine and testes; several clinico-chemical plasma parameters were also determined. RESULTS As was to be expected, the rats lost a considerable amount of weight on the energy-reduced diet. At the same time a shift occurred in the ratio of fat to protein in favour of protein in the carcass, leading to a marked reduction of body fat levels and a slight reduction of protein levels. There were, however, no significant differences between the control group and the treated group (with L-carnitine supplementation) with regard to any of these parameters. The clinico-chemical parameters measured in plasma (glucose, triglycerides, total cholesterol, free fatty acids, 3-hydroxybutyric acid) also showed no differences between the groups. CONCLUSIONS The rat model used here did not show a positive effect of L-carnitine supplementation on weight loss and body composition of rats fed an energy-deficient diet. The animals' endogenous carnitine synthesis was obviously adequate to ensure efficient beta-oxidation of fatty acids during the catabolic phase.