The 5-HT1A and 5-HT2 receptor affinity of a set of 44 N-alkylated 1-aryl-piperazines and their analogs has been analyzed: the n-hexyl derivatives were the most potent and the most selective 5-HT1A ligands of all the investigated N-alkyl homologues. The alkyl chain may stabilize the 5-HT1A receptor-ligand complex by hydrophobic forces. A set of the alkyl substituent contributions (CHT1A) for prediction of the 5-HT1A affinity of N-alkyl derivatives of 1-arylpiperazines and related compounds have been defined on the basis of the Free-Wilson analysis.