The interaction of the amino acid beta-(N-methylamino)-L-alanine, a neurotoxin found in the seed of the false sago palm, with erythrocyte membranes has been monitored by electron paramagnetic resonance techniques of spin labeling. This neurotoxin did not alter the motion or order of bilayer lipids, but a highly-significant and dose-dependent alteration in the physical state of cytoskeletal proteins was observed. These results are discussed in reference to potential mechanisms involved in the neurotoxicity produced by beta-(N-methylamino)-L-alanine and in reference to the unusual neurological disorders among the Chamorro population of Guam and other Marianas Islands.