Abstract: Objective To determine the antigenicity of the influenza viruses,isolated from influenza-like pat ients during outbreaking and epidemic seasons in 1998 and 1999,and to investigate the immunity of Hang zhou population to different influenza viruses.Method Cross haemag glutination inhibition(HI)test and HI test were adopted.Results Twelve isolates of influenza virus were isolated in 1998 and 1999 in Zhejiang province.Among them,11 viral isolates fell into the subtype of A₃ and one into the influenza B virus.Antigenic rates of A₃/Zhejiang/10/98 to A₃/ Wuhan/359/95,to A₃/Sydeny/5/97,and to A₃/Shang hai/1/98 were 1.4,4.0 and 16.0,respectively,while those of A₃/Zhejiang/ 7/99,to the three standard viral isolates described above were 22.6,2.0 and 1.4,respectively.The mono-direction HI titers of B/Zhejiang/31/99 to B/Beijing/172/97,and to B/Shenzhen/12/ 97 were\10240 and 40,respectively.Population in Hangzhou had HI antibody to different influenza viruses with positive rates of 62.4%~100.0%,and GMT ranged from 11.67 to 275.49.Conclusion With the exception of A₃/Zhejiang/10/98 similar to A₃/ Wuhan/359/95,all the viral isolates in the subtype of A₃ were similar to A₃/Shanghai/1/98 in ant igenicity.The antigenicity of influenza B virus isolated was similar to Panama-like virus.The majority of Hangzhou population has resistance to both influenza A (H₃N₂)and B Panama-like viruses.