We have cloned, sequenced and mapped a gene ( sod-2 ) encoding manganese superoxide dismutase [EC 1.15.1.1] from the nematode Caenorhabditis elegans . The sod-2 was mapped to chromosome I by hybridization with a YAC polytene filter. The protein-coding region spans 1129 base pairs including 4 introns and encodes a protein of 221 amino acids (aa) (Mr = 24536) of which the first 24 aa are the presumed mitochondorial-targeting signal peptide. The gene sequence of sod-2 was slightly different from an isoform, sod-3 .