Blends of isotactic and syndiotactic polypropylene were studied by differential scanning calorimetry (d.s.c.), light transmission measurements and pressure-volume-temperature (PVT) measurements. D.s.c. measurements show the absence of any kind of melting point depression in the blends. Furthermore, the change of the ratio of crystallized i-PP and crystallized s-PP in the blends as a function of crystallization temperature is discussed. PVT and light transmission measurements reveal that the rate of crystallization depends stronger on the crystallization temperature for i-PP than for s-PP. Thus at higher degrees of supercooling the crystallization of i-PP is faster and at lower supercoolings s-PP is able to crystallize faster.