The morphology of injection-moulded high-density polyethylene/polyamide-6 (25/75 vol%) blends, with and without compatibilizer, is investigated both throughout the sample and in the weldline region. A detailed morphological analysis of the skin and weldline using scanning electron microscopy and image analysis established : (a) a significant skin/core effect, (b) a diminution of the thickness of the skin and weldline regions with interfacial modification, and (c) an apparent absence of the minor phase in the skin and weldline. Subsequent more detailed work indicated that there was, in fact, no absence of the minor phase in the skin and weldline. The existence of a morphological variation with respect to the thickness (dispersed phase is highly oriented in the subskin and spherical in the core) is clearly shown in this study. X-ray photoelectron spectroscopy and differential scanning calorimetry of microtomed layers from the surface were used as additional techniques to show that the surface and the weldline region composition of dispersed phase is very close to the original, as-prepared, composition (25/75 vol%). Transmission electron microscopy reveals the presence of a very fine dispersed phase in the skin with particle dimensions almost one order of magnitude smaller than in the core. The interfacial modifier, a poly(ethylene-methacrylic acid-isobutyl acrylate) ionomer, was found to reduce the size of the dispersed phase, the skin thickness and the width of the weldline. The dimensions of the regions with very fine dispersed phase (skin and weldline) correlate well with those observed in the advancing melt front as analysed in the short-shot samples. Less coalescence and a more stable morphology is observed.