The ability of sumatriptan (GR 43175; 3-[2-dimethylamino]ethyl-N-methyl-1H-indole-5 methane sulphonamide) to interact with 13 neurotransmitter receptor sites was determined using radioligand binding techniques. Sumatriptan displayed the highest affinity for 5-HT1D (Ki = 17 nM) and 5-HT1B (Ki = 27 nM) binding sites and was slightly less potent at 5-HT1A binding sites (Ki = 100 nM). By contrast, sumatriptan was essentially inactive (Ki greater than 10,000 nM) at each of the 10 other binding sites analyzed. These data indicate that sumatriptan interacts selectively with 5-HT1B and 5-HT1D sites and suggest that these interactions may be the basis of its apparent efficacy in the acute treatment of migraine.