The enthalpies of micellization for the anionic surfactant sodium dodecylsulphate (SDS) in water and in NaCl solution have been studied by calorimetry at 298 K. The calorimetric experiments were carried out by measuring the heat of solution of SDS in both monomeric and micellar phases, From these data the enthaply of micelle formation was derived. The enthalpy of solution of SDS below and above the critical micellar concentration was found to be endothermic. The results indicate that the enthaply of micelle formation in water at 298 K is - 1.42 +/- 0.30 KJ mol(-1). The micellization process becomes more exothermic with addition of salt and the enthalpy of micelle formation in 0.50 mol dm(-3) of NaCl is - 8.90 +/- 0.15 kJ mol(-1), The calorimetric ampoule-breaking technique was adopted in this work for the investigation of the enthalpy of SDS micelle formation, Titration microcalorimetry using the TAM was unsuccessful. The enthalpy of micellization of SDS in water obtained in this work corresponds to the sign of the majority of the values reported in the literature, although very different values are found as well. An evaluation of the thermodynamic parameters is given.