Deletion mutants of the serotonin HT2 receptor have been constructed in which the N- and C-terminal sequences have been gradually removed. The mutant constructs were assayed for their biological activity by electrophysiological measurements in Xenopus oocytes previously injected with the respective in vitro synthesized cRNAs. No significant loss of biological activity was observed when either the extracellular N-terminal sequence, including all potential glycosylation sites, up to the beginning of the first transmembrane domain or the C-terminal sequence up to cystein residue 397, which is conserved in most G-protein coupled receptor known so far, was deleted from the serotonin HT2 receptor constructs.