A poly(ether ester) thermoplastic elastomer with a soft block content of 50 wt % has been studied with synchrotron small-angle X-ray scattering (SAXS) during strain/relaxation cycles. The rigid nodes of the elastic network are not the hard domains themselves but instead are ordered three-dimensional assemblies of several hard domains. At a critical elongation, single hard domains are disrupted and dislocated from these assemblies in a peculiar manner. In the ultimate structure, remaining pairs of hard domains form (semi)elastic nodes. The complex two-dimensional SAXS patterns indicate stacks from tilted lamellae that are destroyed when the sample is strained to double its initial length. With multidimensional chord distribution function analysis, the complex nanostructure and its evolution in the draw experiment have been analyzed. The fundamental hard domains are not lamellae but cylinders (5 nm x 8 nm) arranged on a lattice at cylindrical coordinates (r(12), r(3)), which are given by the intersections of r(3)(r(12)) = +/-1.5r(12) +/- 13nmn, n being a natural number. A semielastic component is made from hard domains forming other lamellar assemblies, which are characterized by n = 3/2. (C) 2003 Wiley Periodicals, Inc.