The hERG K ? channe l under goes rapid inac- tivation that is mediated by ‘collapse’ of the selectivit y filter, ther eby preve nting ion conduc tion. Previ ous stud ies have sugges ted that the p ore-helix of hERG may be up to seven residues longe r than that predicted by homo logy with channe ls with know n crystal str uctures. In the pres ent work, we determin ed structura l features of a peptide from the pore loop region of hE RG (resid ues 600– 642) in both sodium dodecy l sulfate (SD S) and dodecy l phospho chol ine (DPC) micel les using NM R spectro scopy. A comple te structu re calcul ation was done for the peptide in DPC, and the localiza tion of residue s inside the micell es were ana- lysed by using a water -soluble p aramagnet ic reag ent with both DPC and SDS micel les. The pore-hel ix in the hERG peptide was only tw o–four residue s longe r a t the N-ter- minus, compared with the pore helice s seen in the crystal structu res of other K ? channe ls, rather than the seven residue s sugges ted from previ ous NMR studies. The helix in the peptide spanned the same residue s i n both micellar environm ents despite a differ ence in the localiza tion inside the respect ive micel les. To determ ine if the extensi on of the length of the helix was aff ected by the hydroph obic environm ent in the tw o types of micell es, we comp ared NMR and X-ray crystall ography results from a homo lo- gous peptide from the voltage gated po tassium channel, KcsA