Secondary (specific) granules are peroxidase-negative and rich in antimicrobial substances (Joiner et al. 1989, Rorvig et al. 2012). They are more irregular and elongated in form than azurophil granules (Bainton et al. 1971). This might reflect volume adjustment in azurophil granules, which are known to proteolytically process a significant fraction of the proteins that are targeted to them, while little or no processing and therefore no increase in osmotic activity due to proteolysis has been observed in secondary granules (Borregaard & Cowland 1997). Secondary and tertiary granules have overlapping contents but can be discriminated by their intrinsic buoyant densities when centrifuged on gradient media (Kjeldsen et al. 1994).