AbstractIn human freshly prepared platelets the following lysosomal enzymes were studied: α‐mannosidase, α‐fucosidase, β‐galactosidase, β‐glucosidase, β‐glucuronidase, β‐N‐acetylglucosaminidase and acid phosphatase. For each of the examined enzymes the conditions providing maximal activity (pH, buffer), kinetic parameters (saturating substrate concentration and Km) as well as heat stability were established. On the basis of these parameters it is suggested that many of the serum glycohydrolases may be platelet derived.