Dystrophin is a muscle cytoskeletal protein with a molecular mass (MM) of approximately 420 kDa and an isoelectric point (pI) of approximately 5.5, which is abnormal in size and/or abundance in Becker muscular dystrophy (BMD). We investigated the abnormality of dystrophin molecule in muscles biopsied from 23 BMD patients using the two-dimensional gel electrophoresis (TDGE). We found 7 protein spots which reacted specifically with the monoclonal anti-dystrophin antibody (mAb) A1C raised against N-terminal domain of the normal dystrophin. These spots were focused on the two-dimensional gel at the same position as the normal dystrophin (#1), at the position with MM approximately 480 kDa/pI approximately 5.35 (#2), the position with MM approximately 400-330 kDa/pI approximately 5.51-5.47 (#3), the position with MM approximately 300 kDa/pI approximately 5.4 (#4), the position with MM approximately 235-250 kDa/pI approximately 5.53-5.5 (#5), the position with MM approximately 165 kDa/pI approximately 6.0 (#6), and the position with MM approximately 160 kDa/pI approximately 5.75 (#7). These spots were classified into five patterns in individuals, that is, #1 alone in 3 patients, #3 alone in 1, the combination of #3 and 5 in 17, the combination of #1, 3 and 5 in 1 and the combination of #1, 2, 4, 6 and 7 in 1. The combination of #3 and 5 was observed in 17 of 23 patients (75%).(ABSTRACT TRUNCATED AT 250 WORDS)