Male Sprague-Dawley rats, aged 2, 5, 16, 20 and 30 months and normally fed, were used for determination of carnitines in the brain, serum, heart, tibial muscle, liver and urine. With respect to 5-month-old animals, those aged 30 months exhibited a statistically significant decrement of total carnitine levels in the brain, serum, heart and tibial muscle, accompanied by a dramatic increment in the liver. This suggests impaired net transport of carnitines from the liver to the blood in old age. Urinary excretion was similar in the two age groups. One group received from 5 months on daily 75 mg/kg acetyl-L-carnitine in drinking water. At 20 months, the treated animals showed levels of brain, heart and serum carnitines similar to those of 5-month-old animals. The recovery of brain, heart and serum carnitines in the old animals treated with acetyl-L-carnitine indicates that intestinal absorption and tissue uptake remain sufficiently efficient in the course of aging. The lower level of brain lipofuscins due to acetyl-L-carnitine treatment may be related to the effect of the compound on acetylcholine metabolism.