Many plants and the plant-derived honeybee propolis have shown biological activities like immunomodulation and antitumor effect. The effect of two water-soluble propolis derivatives (WSDP) from Croatia and Brazil, caffeic acid, quercetin, chrysin and naringenin which are present in WSDP was assessed on the development of Ehrlich ascites tumor (EAT). The compounds (50 mgkg(-1)) were given by gastric intubations (po) 2 h prior to the intraperitoneal injection of EAT (2x10(6)) cells. It was observed that WSDP and its compounds effectively inhibited tumor growth and proliferation of EAT. The volume of ascitic fluid induced by EAT cells and total number of cells present in the peritoneal cavity was markedly reduced in EAT-bearing mice treated with test components. Treatment with test components increased the number of polymorphonuclear (PMN) cells and decreased the number of macrophages in the peritoneal cavity of treated animals. The macrophage spreading activity revealed that WSDP and all test compounds affected the functional state of macrophages increasing their tumoricidal activity. The effect of WSDP was most pronounced suggesting synergistic effect of components present in WSDP. It is likely that part of the antitumor efficacy of the assayed components against EAT cells was the results of increased macrophage activity.