(PPE/PS)/PA6 and PS/PA6 blends were prepared by means of melt-extrusion. They were compatibilized using the reactive styrene-maleic anhydride copolymer with 2 wt% maleic anhydride (SMA2). The effect of compatibilization on the phase inversion and the stability of the resulting co-continuous blend structures were investigated using scanning electron microscopy, dissolution and extraction experiments. The onset of co-continuity shifted towards lower PA6 concentrations according to the change in blend viscosity ratio. The melting order of the components inside the extruder could result in a change in the observed co-continuity interval in slowly developing phase morphologies. The unmodified co-continuous blends were not stable and did break-up into a droplet/matrix type of morphology upon annealing in the melt depending on the blend composition. Although the stability of the threads during annealing improved upon compatibilization because of the lower resulting interfacial tension, the decreased possibility for recombination and coalescence during flow reduced the co-continuous region for the compatibilized blends. It is proposed that a dynamic equilibrium between break-up and recombination phenomena after the initial network formation is necessary to maintain the network structure. (C) 2004 Elsevier Ltd. All rights reserved.