A micro-combustion calorimeter suitable for samples of mass about 10 mg to 50 mg is described. Calibration with benzoic acid led to the energy equivalent epsilon degrees = (1809.82 +/- 0.28) J.K-1 The calorimeter was tested by determining the standard molar enthalpies of formation at the temperature 298.15 K of salicylic acid : Delta(f)H degrees(m){o-C6H4(OH)(CO2H), cr} = -(587.8 +/- 1.5) kJ.mol(-1) and of urea : Delta(f)H degrees(m)(H2NCONH2, cr) = -(333.4 +/- 0.6) kJ.mol(-1).