Most of dystrophin, the protein product of the Duchenne muscular dystrophy locus, is composed of spectrin-like repeats, suggesting that dystrophin is an elongated cytoskeletal molecule (Davison, M. D., and Critchley, D. R. (1988) Cell 52, 159-160; Koenig, M., Monaco, A. P., and Kunkel, L. M. (1988) Cell 53, 219-228). We present here a detailed analysis of the repeat domain of human dystrophin and propose that it is composed of 24 rather than 26 repeat units as previously suggested. Moreover, spacer sequences which do not align with the repeat consensus are present at the beginning and at the end of the repeat domain. Two other non-repeat spacers are found between repeat elements 3 and 4 and 19 and 20. The high proline content of each spacer suggests that it might represent a hinge. Using five new anti-dystrophin antisera and two previously described antisera (Hoffman, E. P., Brown, R. H., Jr., and Kunkel, L. M. (1987a) Cell 51, 919-928) to detect different dystrophin peptides after proteolytic cleavage, we show that the four hinge segments are sensitive sites for proteolysis. We present a model for a membrane-associated network of dystrophin in which the hinges play a key role by conferring flexibility to the network and thus resilience to the membrane.