The cytoplasmic matrix is physically linked with the intramembranous orthogonal assemblies of particles of astrocytes. The assembly particles are invariably associated with the P or cytoplasmic face of the plasma membrane, never the E or external face. The assemblies are redistributed by agents that affect the structure of cytoplasmic proteins. Thus, after incubation of primary cultures of astrocytes in cytochalasin B and D, which dissociates actin filaments, the assemblies clump so as to form large rafts throughout the membrane. Colchicine and vinblastine, which disaggregate microtubules, cause the assemblies to "cap": migrate to one pole of the cell. In the center of focal lesions of the cerebral cortex in young rats, made with a cold (-80 degrees C) probe, the assemblies and background particles closely resemble those after denaturation with guanidine or urea: the assemblies become so tightly clumped that the background particles are excluded and the periodicity of the subunits may be reduced. In the astrocytes at the periphery of the gliotic scar, the assemblies increase in number, but do not clump.