Thermally stabilised, unpigmented, rigid PVC samples, were exposed to accelerated photoageing at 40 degrees C, 55 degrees C and 70 degrees C. The concentration profiles of photoproducts were determined on microtome slices (similar to 20 mu m) parallel to the irradiated surface using IR (carbonyls) and UV (polyenic double bonds) spectrophotometry and by steric exclusion chromatography (M-n and M-w). They indicate that carbonyls and chain scissions predominate only in a thin superficial layer whereas polyconjugated double bonds and crosslinks predominate in a subcutaneous layer (similar to 300-400 mu m). Tensile measurements show that the ultimate elongation decreases after an induction period whose duration is a decreasing function of temperature. The change of mechanical behaviour can be described in terms of a ductile-brittle transition shift, mechanism in which crosslinking plays an important role. A tentative explanation of a such crosslinking induced transition is proposed in the discussion.