Dynamic nuclear polarization (DNP) has proved to be one of the most effective methods to increase the nuclear spin polarization in inorganic as well as organic materials since several decades. In combination with methods to rapidly dissolve the polarized solid sample it is possible to obtain a solution of molecules containing hyperpolarized nuclei. This has enabled new applications in Nuclear Magnetic Resonance (NMR) spectroscopy as well as medical applications in Magnetic Resonance Imaging (MRI). We studied the dynamic nuclear 13 C polarization in solid [1-13 C] pyruvic acid doped with the trityl radical AH 111 501 at different temperatures and magnetic fields. The measurements were performed in a 4 He evaporation refrigerator operated inside a superconducting solenoid system. Working points at temperatures between 900 and 1350 mK have been adjusted and the polarization measurements have been performed at magnetic fields of 2.5, 3.5 and 5 T, respectively. This set of measurements allows to draw a clear picture of the temperature and magnetic field dependency of the 13 C polarization within the given range. The highest polarization measured was 74.7% at a temperature of 900 mK in a magnetic field of 5 T.