Abstract: During 1982-1990,a longitudinal observation on prevalence trend of malayan filariasis has been made in endemic areas with An.anthropophagus as the main vector.A total of 22 795 person-times of blood examination were made,and 30 439 An.anthropophagus and 10 061 An.sinensis were dissected respectively.The microfilaraemia rate dropped from 1.0% to 0.14%,and the infection rate of An.anthropophagus decreased from 0.74% to 0.09% in 3 endemic villages,while no positive case or infected vector occurred in 5 villages where microfilaraemia cases were absent since the beginning of the study.In a cross-sectional survey,855 villages of 17 counties has been monitored for 10 years.Out of 213 934 person-times of blood examination,only 56 were positive,the average microfilaraemia rate being 0.0262%,and 94.64% of the positive had already been detected before 1986.Based on these data,it has been suggested that in endemic areas with An.anthropopha gus as main vector,when the microfilaraemia rate dropped to1% after control,there was no indication that the rate would upgrade during the survey period.A decline trend of the transmission of malayan filariasis,therefore,has been exhibited.