A double-stranded cDNA molecule which includes DNA encoding human manganese superoxide dismutase has been created. The sequence of one strand of a double-stranded DNA molecule which encodes human manganese superoxide dismutase has been discovered. Such molecules may be introduced in procaryotic, e.g., bacterial, or eukaryotic, e.g., yeast or mammalian, cells and the resulting cells cultured or grown under suitable conditions so as to produce human manganese superoxide dismutase or analogs thereof which may then be recovered. By this invention, human MnSOD gene fragments from various plasmids may be ligated to yield a complete genomic human MnSOD gene fragment. Human MnSOD or analogs thereof may be used to catalyze the reduction of superoxide radicals, reduce reperfusion injury, prolong the survival time of isolated organs, or treat inflammations. The invention also concerns a method of producing enzymatically active human manganese superoxide dismutase or an analog thereof in a bacterial cell which contains and is capable of expressing a DNA sequence encoding the superoxide dismutase by maintaining the bacterial cell under suitable conditions and in a suitable production medium. The production medium is supplemented with an amount of Mn++ so that the concentration of Mn++ in the medium is greater than about 2 ppm. Genomic MnSOD DNA should also be capable of expression in eucaryotic cells under suitable conditions. This invention also concerns a method of recovering purified enzymatically active manganese superoxide dismutase from bacterial cells. It should also be possible to recover manganese SOD from genomic MnSOD DNA expressed in eucaryotic cells using similar methods.