This paper reports the results of a microcalorimetric study of the oxidation of L-ascorbic acid in solution. The study of the oxidation reaction was carried out under varying conditions of pH, oxygen concentration, ascorbic acid concentration, temperature, addition of ethylene-diaminetetraacetic acid (EDTA) and addition of a radical scavenger. From these results it is proposed that ascorbic acid is oxidised in solution by molecular oxygen via an ascorbic acid radical, formed from the interaction of ascorbic acid and free metal in solution. The oxidation product, dehydroascorbic acid, then goes on to form other products by hydrolysis. The change in enthalpy associated with the oxidation reaction was determined as - 130.9 kJ mol(-1) and the reaction has a first order rate constant, with respect to the oxygen concentration, of 1.8 x 10(-4) s(-1). The rate of oxidation was found to increase with pH, oxygen concentration and concentration of metal in solution.