Dramatic morphological changes have been found in the blend of an aliphatic crystallizable polyamide (nylon 6/6) with trace quantities of a polar non-crystallizable diluent (poly(vinyl pyrrolidone)). The influence of the addition of PVP on the crystal morphology of nylon 6/6 was studied using d.s.c., X-ray (small and wide angle) and hot stage optical microscopy. The addition of the diluent has a dramatic effect on the spherulitic morphology of nylon 6/6 by causing a striking reduction in the nucleation density of spherulites, modification of lamellar organization in spherulites (as evidenced by the occurrence of banding), and modification of interlamellar spacings. Furthermore, the effect of increasing diluent molecular weight was studied, and it was shown to have only a subtle affect on the system.