A comparison was made of the host (BALB/c mice)-parasite relationship of a Chinese mainland (Anhui) strain and Philippine (Sorsogon) strain of Schistosoma japonicum. Differences in fecundity, infectivity, prepatency, host survival and susceptibility to praziquantel were examined. The mean percentage of worms establishing was 40.0 and 34.4% for Chinese and Philippine S. japonicum, respectively. Egg laying commenced on days 26 and 28 after infection with the Chinese or Philippine strain, respectively. Significant differences in the total number of eggs and number of eggs per worm pair laid were observed. In terms of the number of eggs per worm pair and host survival, the Chinese strain was more virulent than the Philippine in BALB/c mice. Praziquantel treatment reduced worm burdens by 80-90% in both strains. No significant differences were observed in murine antibody responses against the 2 strains. Irradiated Chinese cercarial vaccines were protective only against homologous challenge; irradiated Philippine cercarial vaccines were not protective, confirming earlier findings that this strain is neither able to induce nor able to act as a target of irradiated cercariae-mediated vaccination. Antibody responses and immunoblot profiles in vaccinated mice were similar, regardless of the strain of parasite used.