Substituting a furan, a thiophene, a benzo[b]furan, a benzo[b]thiophene, or a quinoline ring for the p-chlorophenyl moiety of baclofen has led to GABAB ligands with different affinities depending on the nature of the heteroaromatic ring, and on the nature and position of its substituent. As steric effects cannot account for all the affinity variations, we have studied the lipophilic and electronic properties of baclofen and selected 3-heteroaromatic analogues, gaining insight into the structural features necessary for GABAB affinity. Centrifugal partition chromatography (CPC) has been used to measure octan-1-ol water distribution coefficients, while ab initio molecular orbital (MO) calculations were performed to study electronic properties.