The expression of dystrophin and alpha1-syntrophin in rat tibialis anterior muscles were evaluated during a cycle of regeneration after myonecrosis induced by the injection of cardiotoxin. Immunohistochemical studies were performed in cryosections of muscles on days 1, 3, 5, 7, 10, 14, 21 and 28 after injection of cardiotoxin. Western blot analysis was also examined in muscle on days 1, 3, 5, 7, 10, 14, 21 and 28. In immunohistochemical studies, dystrophin was stained weakly at the sarcolemma of some regenerating muscle fibers on day 3, and by day 10 it was stained strongly on almost all regenerating muscle fibers. Alpha1-syntrophin was stained weakly at the sarcolemma of some regenerating fibers on day 5, and by day 14 it was detected on all regenerating muscle fibers. In Western blot analysis, dystrophin (DYS1) and alpha1-syntrophin (alpha1S) were completely absent on day 1. Re-expression of DYS1 and alpha1S was visible by day 5 and accelerated thereafter. The Western blots of DYS1 and alpha1S were densitometrically analyzed on each day. The protein levels on each day were converted to the percentage of the protein level on day 28, which was taken as 100%. From the sequential line based on these data, the following results were obtained on the chronological course of DYS1 and alpha1S. DYS1: 25% of the protein level on day 28 was reached by 3.5 days, 50% was reached by 5.3 days, and 90% was reached by 6.9 days. Alpha1S: 25% of the protein level on day 28 was reached by 4.6 days, 50% was reached by 6.0 days, and 90% was reached by 12.5 days. In this study, DYS1 regenerated earlier than alpha1S at the sarcolemma of regenerating muscle fibers.