Fukuyama-type congenital muscular dystrophy and congenital muscular dystrophy 1C are congenital muscular dystrophies that commonly display reduced levels of glycosylation of alpha-dystroglycan in skeletal muscle. The genes responsible for these disorders are fukutin and fukutin-related protein (FKRP), respectively. Both gene products are thought to be glycosyltransferases, but their functions have not been established. In this study, we determined their subcellular localizations in cultured skeletal myocytes. FKRP localizes in rough endoplasmic reticulum, while fukutin localizes in the cis-Golgi compartment. FKRP was also localized in rough endoplasmic reticulum in skeletal muscle biopsy sample. Our data suggest that fukutin and FKRP may be involved at different steps in O-mannosylglycan synthesis of alpha-dystroglycan, and FKRP is most likely involved in the initial step in this synthesis.