Thermochemical measurements were made of the reactions between sodium cyclohexyl dithiocarbamate, potassium n-butyl xanthate and mixtures thereof with pyrite at pH = 4, The initial steady state heat of adsorption for the potassium n-butyl xanthate and sodium cyclohexyl dithiocarbamate was -67 kJ/mole, When a mixture of these reagents was used this increased to -90 kJ/mole. in all cases the pH increased during the experiments, When FeSO4 replaced the pyrite the Delta H for the xanthate decreased to -43.9 kJ/mole, The results indicated that for the xanthate, the metal thiolate was formed and subsequently oxidised to dixanthogen. The latter reaction did not occur in the case of the dithiocarbamate, however the extent of the first reaction between the dithiocarbamate and pyrite was controlled by proton availability, For the mixture of reagents it is proposed that the dithiocarbamate adsorbs preferentially due to its faster adsorption kinetics and the more stable nature of the surface complex. The dixanthogen species formed then aggregates around the ＇＇anchors＇＇ and results in enhanced hydrophobicity, This will contribute towards the enhanced flotation performance obtained when mixtures of collectors are used [1].