Abstract: Optically active bases are prepared by reacting the racemic base with an optically active half amide of an unsaturated aliphatic dicarboxylic acid of the formula ##STR1## where R.sub.1, R.sub.2 and R.sub.3 are the same of different and are hydrogen, halogen, a hydroxy group, a methyl group or a methoxy group or two of R.sub.1, R.sub.2 and R.sub.3 together are a methylenedioxy group, R.sub.4 is hydrogen or a methyl group, R.sub.5, R.sub.6 and R.sub.7 independently are hydrogen or a C.sub.1 -C.sub.4 alkyl group and n is 0 or 1 and optionally splitting an optically homogeneous salt fraction into the corresponding optically active base and the added half amide.