Ammonia adsorption microcalorimetry studies have shown that for ZSM-5-based materials, whose XRD crystallinity was varied from 3 to 70%, the number of strong Bronsted acid sites, that is those with a DeltaH(ads) between 120 and 140 kJ/mol, increases with increasing XRD crystallinity. A strong correlation was observed between the catalytic activity of these zeolite-based materials in terms of the demanding n-hexane, cracking reaction and the number of strong acid sites. For samples with XRD crystallinities below 30%, however, the number of strong acid sites is disproportionately low and the catalytic activity only becomes significant at crystallinities above this level.