Solution and mixing enthalpies for the orthophosphoric acid (H3PO4)-N,N-dimethylformamide (DMF) system were measured over the whole concentration range at 25 degreesC. The standard value of solution enthalpy of phosphoric acid in DMF and the standard transference enthalpy of H3PO4 from water to DMF were calculated. The mixing enthalpy concentration dependence permitted making assumptions on complex formation in the system under investigation. (C) 2003 Elsevier Science B.V. All rights reserved.