In order to produce high proton polarizations, several organic hydrocarbons have been doped with stable free radical molecules. Through the "solid state effect" a part of the electronic polarization in a magnetic field has been transferred to the protons of these materials. For this purpose, the "forbidden electronic transitions" of the combined electron-proton system have been saturated at about 37 GHz. The enhancement factor of the dynamic proton polarization was measured by pulsed NMR at 56 MHz. In phenanthrene with about 4 w.% bis-diphenylen-phenylallyl (BPA) a maximum polarization of 10.5% has been obtained at 1.5 °K and 13 200 gauss. This value may be increased by extending the temperature and magnetic field range. Systematic investigations in numerous organic systems have been carried out and have particularly yielded data on the frequency dependence and on the saturation behaviour of the enhancement curves. - Spin temperature theories of dynamic polarization have been considered to explain the results and to find possibilities for improving the polarization. In particular, the exchange interaction of the radicals and the distinction between relaxing and polarizing paramagnetic centres had to be taken into account.