The profibrinolytic and antithrombotic glycosaminoglycan heparan sulfate (HS) was tested in vitro on some neutrophil functions induced by several stimuli. HS 1-500 micrograms/ml was able to significantly inhibit, in a dose-dependent fashion, superoxide anion generation, lysozyme and beta-glucuronidase release from neutrophils stimulated with the formylated oligopeptide fMLP, the ionophore A23187, and Platelet Activating Factor. Such an effect could represent an additional therapeutical benefit in those pathological conditions in which neutrophil activation contributes to tissue injury and vascular damage.