The thermochemistry of adenosine(cr) was studied by a variety of methods: the standard (pressure p degrees = 0.1 MPa) molar enthalpy of combustion in oxygen at T = 298.15 K was measured by means of combustion calorimetry and was found to be Delta (c)H(m)degrees = -(5139.4 +/- 3.3) kJ . mol(-1); the standard molar heat capacity C(p,m)degrees was determined by means of adiabatic calorimetry for the range 11 less than or equal to (T/K) less than or equal to 328 {C(p,m)degrees = (290.10 +/-0.58) J . K-1 . mol(-1) at T = 298.15 K}; and the saturation molality in water was measured by means of high-performance liquid chromatography and was found to be m(sat) (1.849 +/-0.015) . 10(-2) mol . kg(-1) at T = 298.15 K. Derived quantities at T = 298.15 K for adenosine(cr) are the standard molar enthalpy of formation Delta (f)H(m)degrees = -(653.6 +/-3.6) kJ . mol(-1), the third law standard molar entropy S(m)degrees = (289.57 +/- 0.6) J . K-1 . mol(-1) and the standard molar Gibbs free energy of formation Delta (f)G(m)degrees = -(204.4 +/- 3.6) kJ . mol(-1). The function Phi (m)degrees - Delta TS(m)degrees - Delta (T)(0)H(m)degrees /T for adenosine(cr) was tabulated for 5 less than or equal to (T/K) less than or equal to 320. A thermochemical cycle was used to calculate Delta (f)G(m)degrees = -(194.5 +/- 3.6) kJ . mol(-1), Delta (f)H(m)degrees = -(621.3 +/- 3.6) kJ . mol(-1), and m S(m)degrees = (364.6 +/- 0.7) J . K-1 mol(-1) for adenosine(aq) at T = 298.15 K. These values in turn were used to calculate standard molar formation properties at T = 298.15 K and ionic strength I = 0 for the adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP) series of aqueous species. Standard molar transformed formation properties for the aqueous biochemical reactants adenosine, AMP, ADP, and ATP have also been calculated at T = 298.15 K, PH = 7.0, pMg 3.0, and I = 0.25 mol . kg(-1).