Abstract: To evaluate the safety,immunogenidty and pretective efficacy of HFRS-1 vaccine purified from sucking mouse brains a controlled field trail was carried out in the endemic area of HFRS in Zhejiang province form August 1995 to September 1998.10178 volunteers were vaccinated while 16203 people living in the same areas were chosen as control group.The side effect of the vaccine was slight except for the high incidence of local pain caused by.No severe general reaction was ever found Two weeks after three doses the seroconvertion of the IFA and neutralizing anti-Hantaan virus were 100% (86/86) and 44.44% (8 18) respectively.Just bdfore booster one year after the basic immunization the positive rate of IFA and PRNT dropped to 28.57% and 14.80%.Two weeks after the booster both rates rebounded to 83.33% and 56.56% respectively.The changes of geometric mean titre(GMT) were probably the same.Two years after the booster the seroprev-elence of IFA and PRNT was 22.1% and 19.35%.During the three-year kobaervation no HFRS patients weire found among the.accinees who received whole schedule vaccination ecept for one case who received only two doses patients were found in the control group the epidemiological kprotective rate for three years was 95.70%.In short the result suggested that the vaccine was safety and has good pretective effects.Idt may has immunological in-hanced reaction but we did find infectiousinhanced reaction in our study.It seems that the implementary injection and further observation are of great importance.