Effect of two preparation (Croatian and Brazilian) of water-soluble derivative of propolis (WSDP), caffeic acid, quercetin, chrysin, naringenin (components present in WSDP) on the development of Ehrlich ascites tumour (EAT) was evaluated. Test components (50 mg/kg) were given perorally or intraperitoneally 2 h prior the intraperitonel injection of EAT (2 x 10(6)) cells. It was observed that all test compounds effectively inhibited tumour growth and the 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. In treated mice the number of polymorphonuclear (PMN) cells in the peritoneal cavity was increased while the number of macrophages was decreased. The macrophage spreading activity revealed that WSDP and all test compounds affected the functional state of macrophages increasing their tumorcidal activity; the effect of WSDP was most pronounced indicating synergistic effect of components present in WSDP. Antitumor activity of WSDP may be the result of different specific mechanism(s) of flavonoids present as compared to individual flavonoid given alone. It is likely that the part of antitumor efficacy of test components against EAT cells was the results of increased activity of macrophages.