Reliable experimental data for semicrystalline polymers crystallized under pressure are supplied on the basis of a model experiment in which drastic solidification conditions are applied. The influence of the pressure and cooling rate on some properties, such as the density and microhardness, and on the product morphology, as investigated with wide-angle X-ray scattering (WAX-S), is stressed. Results for isotactic polypropylene (iPP) samples display a lower density and a lower microhardness with increasing pressure over a wide range of cooling rates (from 0.01 to 20 degreesC/s). Polyamide-6 (PA6) samples exhibit the opposite behavior, with the density and microhardness increasing at higher pressures over the entire range of cooling rates investigated (from 1 to 200 degreesC/s), A deconvolution technique applied to iPP and PA6 WAXS patterns has allowed us to evaluate the final phase content and to assess the crystallization kinetics. A negative influence of pressure on the a-crystalline phase crystallization kinetics can be observed for iPP, whereas a slightly positive influence of pressure on the crystallization kinetics of PA6 can be noted.