Thermal behavior of two hydrofullerenes, C60H36 and C60H18, was studied by means of Knudsen cell mass-spectrometry and infrared spectroscopy. Vapor pressures and enthalpies of sublimation at T = 550-685 K were measured. Sublimation of the hydrofullerenes was accompanied by partial loss of hydrogen. Decomposition of C60H36 was confirmed to be a stepwise process with formation of C60H18 as an intermediate product. The material of the Knudsen cell strongly affected the partial pressures and mass-spectra of the hydrofullerene vapor species.