In the present study the hematological effects of a sustained release chitosan formulation of pentoxifylline (CAS 6493-05-6) were examined and compared with those of a commercial product. The study was carried out on 12 healthy volunteers. Both formulations were tolerated well clinically. The results demonstrated no antiaggregatory effect of the two different formulations of pentoxifylline in platelet rich plasma. Both drugs resulted in a decrease of plasma fibrinogen levels. A remarkable side effect of the new formulation was mild basophilia, without any clinical problems.