The size of the vanilloid receptor was examined by high-energy radiation inactivation analysis of the binding of [H-3]resiniferatoxin to pig dorsal root ganglion membranes; it was found to be 270 +/- 25 kDa. This value most likely represents the size of a receptor complex rather than of an individual subunit. Other ligand-gated cation channel complexes have reported molecular weights in this range, e.g. 300 kDa for the acetylcholine receptor.