The excess enthalpies of cyclohexane + cyclohexanone, cyclohexane + methyl methacrylate, and cyclohexanone + methyl methacrylate have been measured at 298.15 K. The H-E values were compared with Prigogine-Flory-Patterson estimations. Both thermodynamic and spectroscopic results support the hypothesis of strong interactions between cyclohexanone and methyl methacrylate. The structure of the methyl methacrylate + cyclohexanone system is discussed.