Abstract: Dengue fever was prevalence in Panyu and other cities of Guangdong Province in 1995．Indirect munofluorescant assay(IFA)was carried out for detecting anti-dengue virus IgG．Of 58 Sera specimenstested，38 were positive and the positive rate was 65.52％(38/58)．C6/36 cell culture was used for virus isolation．Of 51 serum samples of early phase blood，type Idengue virus was isolated in 28 specimens and the positive rate was 54.90％(28/51)．It verified that type I dengue Virus was the cause of this epidemic．There was significant difference between the two positive rates(Xsup2/sup=1.28，P0.05)．IgG was first detected on the third day and its positive rate reached peak in aweek after onset．Patientssera were not able to type because of the high CROSS-reaction among 4 types and the mean geometric titreS of IgG were all above 1:100．In addition．the specificity of IFA in the detection of antidengue virus IgG Was established．9 sara samples of confirmed dengue fever patients were tested．the positive rate of IgG was 100％and their titres were 1:160-1:1280．Of 336 samples of sera other than dengue fever patients．16 were positive (15 samples 1:40:1 sample，1:80)and the positive rate Was 4.76％．The results showed that if the IgG titre reached 1:80 or above，it was helpful in the diagnosis of dengue virus infection，but the diagnosis should be confirmed by virus isolation．The authors concluded that this assay was simple，sensitive，rapid and economical．