Full coding regions for fast type myosin heavy chain (MyHC) isoforms were sequenced from a porcine skeletal muscle to analyze sequence diversity relating to the contractile properties of muscle fibers. An approximately 6-kb fragment for each MyHC was amplified through RT-PCR using isoform type-specific primers, which were designed in the 5' and 3' non-coding regions of the porcine MyHCs. The lengths of deduced amino acid sequences were 1939, 1939, and 1937 for the porcine MyHC-2a,-2x, and-2b, respectively. The entire amino acid sequences were highly conserved among the three MyHCs, except for the 50/20 k junction region (loop 2) which would weakly bind actin molecules. The porcine MyHC-2b possessed different amino acids from MyHC-2a and-2x, in loop1 and ELC binding region. The sequence data suggested the diversity of contractile properties among the porcine MyHC isoforms.