Blends of isotactic polypropylene (iPP) and hydrogenated oligo(cyclopentadiene) (HOCP) were investigated to gain structural information by means of both SAXS and SANS techniques. The composition range (from 30 to 60% w/w HOCP content) and the temperature range (between 25 and 160 degrees C) were chosen in order to cover the miscibility gap in the phase diagram of the material system. In a previous report, blends lying outside the miscibility gap have been investigated and the corresponding SAXS patterns were interpreted in terms of a pseudo-two phase model. For the SAXS patterns, blends lying inside the miscibility gap are rather hard to be interpreted in terms of such a model. On the other hand, SANS patterns display a behaviour that can be directly rationalised in terms of two different coexisting lamellar phases (each corresponding to two domains enriched in either one of the two components). A novel approach is described which allows such a separation of morphological phases. (C) 2000 Elsevier Science Ltd. All rights reserved.