Provided are methods of inhibiting aggregation of amyloid-beta (Aβ)or accumulation of aggregated Aβ using certain guanylhydrazone compounds.Also provided are methods of treating or preventing an amyloid-related diseasein a mammal, methods of treating a subject having Alzheimer's disease,methods of treating a subject at risk for Alzheimer's disease, methodsof inhibiting aggregation or accumulation of a synuclein, methods of treatinga subject having a disease at least partially mediated by synuclein, methodsof treating a subject at risk for a disease at least partially mediated by synuclein,and methods of inhibiting aggregation or accumulation of a protein involvedin a conformational disease, using the guanylhydrazone compounds.