To examine whether the expression pattern of fast-muscle type troponin-T (TnT) isoforms was fixed in cell lineage, breast muscle pieces (pectoralis major) from chick embryos and young and adult chickens were grafted on to chorio-allantoic membrane of 9-day-old chick embryos and cultured until the host embryos hatched out. Muscle fibre formation of the grafts was investigated by histological and immunohistochemical methods with anti-fast-muscle type and anti-slow-muscle type TnT sera, and the expression of fast-muscle type TnT in the grafts from chick embryos and young chickens was studied by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional SDS-PAGE, and immunoblotting. In the chorio-allantoic grafting, the breast muscle initially degenerated forming pyknotic nuclei and hyaline cytoplasm. The surviving cells, which were supposed to be satellite cells, regenerated new muscle fibres of the same type as those of the grafted muscle in respect of TnT isoform expression. Therefore, we considered that the ability to express specific isoforms of TnT was fixed in the satellite cells, and that chorio-allantoic grafting was a useful technique for studying muscle differentiation.