Polymorphic forms of N-hydroxy-3-[4-[[[2-(2-methyl-1H- indol-3-yl)ethyl]amino]methyl]phenyl]-2E-2-propenamide free base and salts thereof are prepared by various processes.本發明係關於以各種方法製備之N-羥基-3-[4-[[[2-(2-甲基-1H-吲哚-3-基)乙基]胺基]甲基]苯基]-2E-2-丙烯醯胺游離鹼及其鹽之多晶型。