Methyl 3-(2,2-dimethylhydrazino)propionate (I) is treated with a methyl halide (II, X = halo) or dimethyl sulfate (II, X = CH3SO4) to give the appropriate trimethylhydrazinium salt (III), which is transferred to 3-(2,2,2-trimethylhydrazinium)propionate (IV) by Amberlite IRA-400 (OH form). After crystallization from ethanol the inner salt is obtained as a dihydrate.