The processes of thrombin-induced gelation of the fibrinogen may be influenced by a variety of factors including phosphorylational state of the fibrinogen. Casein kinase II (CKII) has been shown to phosphorylate fibrinogen in vitro and accelerate gelation of the fibrinogen. In this work, we have demonstrated that CKII and polycationic compounds such as polylysine, spermine, and spermidine synergistically stimulate thrombin-induced gelation of the fibrinogen. These polycationic compounds were also found to increase the stimulatory effects of CKII on the platelet aggregation. Current findings suggest potential role of CKII and polycationic compounds in the process of hemostasis.