THE distributions of dystrophin,dystrophin-related protein'(DRP) and [beta]-spectrin were compared with that of acetylcholine receptors (AChRs) at rat nerve-muscle junctions (NMJs) using immunofluorescence techniques. In sections, monoclonal antibodies (MAbs) to dystrophin and [beta]-spectrin labelled the entire sarcolemma but were concentrated at the NMJs while those to DRP labelled only NMJs. In permeabilized muscle fibres, DRP was precisely co-localized with the AChRs, whereas the zone of high density labelling of dystrophin and [beta]-spectrin extended 0.3-0.4 [mu] m beyond the AChRs. Within the NMJ, the labelling of DRP appeared as a series of interconnecting lines similar to that of AChRs. However, labelling of dystrophin and [beta]-spectrin was consistently more punctate. These data suggest DRP is more closely associated with AChRs than are dystrophin or [beta]-spectrin.