Three dimensional models for the serotonin human 5-HT 1 A , 5-HT 1 D α and 5-HT 1 D β receptors have been constructed utilising the coordinates of bacteriorhodopsin as an initial template. The 5-HT receptor agonists 5-hydroxytryptamine, 8-hydroxy-2-(di-n-propylamino)tetralin, 5-carboxamidotryptamine, 5-hydroxy-N,N,N-trimethyltryptamine and sumatriptan have been docked into the probable agonist binding site of the receptor models between transmembrane domains 3, 4, 5 and 6 in order to validate the proposed models. Detailed interactions of the ligand-receptor complexes are reported. The relative binding affinities of the ligands can be accounted for, in a qualitative sense, from an interpretation of the ligand-receptor interactions.