Quantitative structure-activity relationships (QSAR) were analyzed for 5-HT1 and 5-HT1A affinity data of two series of 1-arylpiperazines. A conformational analysis of the investigated derivatives was performed using CNDO/2 method. It was shown that some 1-arylpiperazines adopt the bioactive conformations, while the others, like 1-(2-alkylphenyl)-piperazines, should exist in the twisted conformations at the receptor sites.