Potential and limits of dynamic mechanical analysis (DMA) as a tool for fracture resistance evaluation of isotactic polypropylenes and their polyolefin blends are presented. A minimum of information about the materials under investigation is a prerequisite to interpret the DMA traces in a right way. Although DMA is, in general, a powerful method to rank materials in term of toughness, care should be taken with (1) nucleated materials (where both intensity and strength of molecular relaxations need to be taken into account in material evaluation) and with (2) visbroken (i.e., peroxyde treated) grades. Except for these cases, the strengths of the principal or secondary molecular relaxation evaluated by DMA and the Charpy impact toughness correlate quantitatively when all the grades of a series exhibit unstable crack propagation. When changes in the macroscopic mode of fracture or in blend morphology occur, only qualitative correlations remain possible. (C) 2004 Wiley Periodicals, Inc.