l-Carnitine occurs naturally as an essential cofactor of fatty acid metabolism which is synthesised endogenously or obtained from dietary sources. In patients with primary carnitine deficiencies, which may be life-threatening, and some secondary deficiencies such as organic acidurias, the exogenously administered compound is clearly beneficial: by abolishing hypotonia, motor skills are improved, as are muscle weakness and wasting. In preliminary clinical trials in patients with ischaemic cardiac disease, therapy with l-carnitine has shown beneficial effects on myocardial function and metabolism and has improved exercise tolerance in patients with angina pectoris-findings which require further substantiation in larger controlled studies. Moreover, while some interesting evidence suggests that l-carnitine may find potential use in such diverse conditions as carnitine deficiencies secondary to prolonged total parenteral nutrition supplementation or chronic haemodialysis, hyperlipidaemias and the prevention of toxicity induced by anthracyclines and valproate, such findings must be regarded as preliminary. Exogenously administered l-carnitine is very well tolerated. Thus, while its role in primary deficiencies is established, with its profile of negligible toxicity l-carnitine is worthy of further investigation to more clearly define its therapeutic applications in a variety of conditions which may be indirectly related to alterations in fatty acid metabolism.