An efficient conformational space search algorithm CONFLEX augmented with a clustering technique was applied to a model of that particular seco acid which successfully cyclized to macrocyclic lactone in Woodward's total synthesis of erythromycin A, with the purpose of finding the folded conformation long supposed to exist in this seco acid. Among 4999 energy minima that have been generated, 270 of them had conformations almost superimposable with those of the dominant forms of the cyclized model, but the combined population of the reactive conformers was only 3.2% of the total. The implications of these observations are discussed.